Having exceeded my braking capacity more than once in a variety of cars (driving fast in the UK bears no relation to driving fast in the US and believe me I've done both) I still say that the initial bite of a drum braked car is better than a disc.  Obviously they fade to oblivion after a few heavy stops and need adjusting every week, but round town I'd almost prefer them to discs if the maintainence were less.

If you can lock the brakes and skid, they are adequate.  Most (and I probably include myself) drivers do not have the ability to brake at 99.99% of the locked wheel rotation speed and reduce the braking effort as the locking level reduces to avoid skidding, so 4-pots are not really neccessary.
If you feel you need vented discs then you either live in the mountains and regularly descend at speed while towing, are on a racetrack (or should be) or want the extra BHP* that they impart.

*BHP:  Bar Horse Power - the amount of extra power that shiny bits bestow on a car when drinking beer at the bar with your buddies.

Sounds like the only upgrade to anything disk brakes is the addition of a booster? Haven't heard anything that would require more. Except: driving in the US has long stretches and significant braking with a car that is fully loaded - 75mph to 10mph several times during a commute and or weekend run. I just can't believe that the tiny 7.5" solid brake disk compares a larger vented disk with more pots in terms of friction capability & or heat dissapation. I am extremely easy on my brakes in general but not afraid to use them to their full capability. That is why I would always go big n vented. I tend to run at higher speeds n loads than most folk so if I get the chance I will try bigger ventEd. May we never encounter the limit of our brake capacity 

SSR FL-II which come in 10x6 +3 or 10x6.5 -3.  Give that black Mini a touch of bosozoku.

Another wheel offset / break combo bullet point.  The red Mini above has drums.  Here' another Mini with   the same wheel, but with discs and W& arches.  Is it safe to assume that the various disc set ups all increase the track by the same amount?

That's good point. And honestly don't think that there will be that much of a difference. I was just venturing on the side of caution. But you have talked me into the 7.5" set.

Yes i know that is why i stated it is not that big of a deal if you fell that you want the bigger brakes with the 13's. I personally do not think you will find that much difference especially if as you stated you run them in the winter when the weather is cooler and roads are slicker.

Malsal. I already have 8.4's and 13x7's.

7.5's two pots with decent pads the good rotors and a servo will be fine with either size wheel you run. If it does bother you it is not that big of a job to run the 8.4's with the 13's.

Well the 4 pots are supposed to deliver a more even braking pressure, and I truly believe that one. 

And the larger brakes for 13's is because of the significantly increased rotating mass. Unsprung weight is pretty tasking on brakes, and the 13's aren't light. Would the 7.5" brakes stop it? I'm positive they would. But how well? Well I'm not racing on the street, so I don't think it's a huge deal, but it would be nice to know. I'm inclined to agree with you that the difference in the real world isn't going to be very noticeable. So maybe you're right... I'm gonna look more into guys that are running 7.5"s with 4 pots. 

Thanks again guys for the input. This is the kind of discussion that makes me like this site. 

Basic mathematics tells you that 7.9" discs have more stopping power than 7.5" discs, however, in the real world I couldn't tell the difference.

Standard 7½" discs with a servo are fantastic.  My old Elf would jump out of the brake test rollers at MoT time every year, and my friend Paul has them on his Union Jack car to great effect.  The unservoed ones on my UJ car are excellent, but do require a bit more pedal effort.
I'm sure that 4-pots are technically better and certainly hold more bragging rights, but again, in the real world I'm not sure they are really neccessary.  Both 2 and 4-pot brakes will lock the wheels.

Why would you need bigger brakes with 13" wheels than with 10" ??
The overall diameter is the same, and the car won't be travelling any faster or weigh any more than with the 10" wheels.

Alex, I'll be honest... I wsa simply going off popular opinion and overall stisfaction. I truly would rather have the 7.5's. I currently have the 8.4"s that came with the car.  I have a servo as well and it will remain in the car so I don't think I'll struggle much with pressure. But what I was concerned with is true stopping power. I know that it will stop the 10's just fine, but if I go with the 10's in the summer months and then switch to 13's in the winter months, I don't want to be down on braking power. 

I would rather have the 7.5 4 pot kit just to KNOW with confidence that whatever wheels I get will fit.  Are you saying that a 7.5" kit with 4 pot alloy calipers and a good braking circuit will put down just as much braking power as the 7.9's? I was not getting the vented kit anyway. I would have had the solid, slotted rotor design anyway. 

I've got standard S discs on a couple of cars and Mini Sport 4-pots on another.
Not really enough difference to warrant the extra money really.

The pedal feels a bit different, but they will both happily lock the front wheels and I've never had fade with either setup.

Alex you mention 4-pots-  I am wondering whether I made a mistake in getting the regular S Brakes instead of going 4-pot.  I'm happy with the S brakes, but still is there a big difference?

Having had to make some subtle adjustments to fit my (factory) mags over (factory) S discs I would suggest you will need an extremely accurate drawings of your assembled hub/brakes and candidate wheels that you could then combine to identify possible interference.  The only other alternative is to physically try to fit the actual wheels to your car.. or rely on the advice of someone who has already done it.

Cheers, Ian

I think the popularity of the 7.9" kit is a bit of a falsehood.
The extra .4" doesn't really make a huge difference in braking power but does restrict the wheel selection.  I couldn't tell the difference between a vented 7.9" setup with 4-pots and the solid 7½" discs with 4-pots on Tubbs - and the calipers are made by the same company.

To fit either kit you need to buy discs and calipers, so the only advantage of the 7.9" setup is you get to reuse the drive flanges.

Why the 7.9 kit vs the 7.5?  Is the 7.9 a 4 pot system and is that a kit that can be bought also to convert drum to disk?

Alex, Thanks for posting that. I should have clarified that my INTENT is to buy the 7.9" non-vented kit. That is why I'm doing a LOT of research on PCD, backspacing, rim profiles, etc so I can make sure they will clear either around or in front of the calipers. My heart isn't set on the 7.9's yet, but they look like a good option. And once I get more information on specific dimensions of both the brake kit and some wheels I'm considering, I'll pull the trigger and buy them both.

Not all 10" wheels will fit over a 7.9" kit - guess how I know.