i know people swap C4 Vette brakes onto their cars, as well as LS1 F body and even duplicate the factory 1LE setup... they are all proven brake choices, but clearing a 15" wheel can be hit or miss..
has anyone ever tried using C3 (63-82) Vette rotors combined with LS1 F body calipers and pads to try to gain some clearance for 15" wheels and still get the benefits of the lighter multi piston calipers? every C3 Vette ever built came with 15" wheels from the factory, but i think it might possibly clear most 15" wheels with the LS1 calipers.
i know why the popular choices are so popular- the 1LE setup was factory issue and the C4 Vette and LS1 stuff is readily available and cheap, and they have a rotor offset that makes it easier to make caliper mounting brackets on most cars. but they didn't come with 15" wheels stock and i know from experience with the later C4 12" brakes on my Nova that most 15" wheels don't clear the calipers on the "front" side of the caliper without a wheel spacer and finding a mini spare that will clear is a chore..

It's a lot of work to change the brakes. I've been looking into the C4 HD (13inch) set up because for all the effort and money I want a big difference. And I'm only doing it because one day I hope to have tires I can't lock up easily with the stock brakes. For auto-x I've got 275/40/17 tires and I can lock them with the stock 10.5 inch brakes but they're not the best tires. If you want to stick with the 15 inch wheels do you really need the extra brakes? What do you want to do with the car?

road racing is one long term goal for the car, but mostly street driving. i'm also planning on ditching the power brake booster and running manual brakes, mostly to simplify things but also to shed a few pounds and open things up under the hood to make it easier to add some triangulated strut tower braces that tie the strut towers to the firewall, and the bigger brakes allow you to use less effort to get more stopping power..
as to why keep it so i can still use a 15" wheel- stealth.. practicality.. just because.. easy to find a mini spare that fits.. you can still get some fairly good tires in a 15" size, and a set of stock car style 15X10 steelies all around would look badass..

I understand all your points. However, to get big enough brakes so you can ditch the booster you may find they won't fit a 15 inch wheel anyway. Unless you have giant legs! BTW there are 3 point braces that fit with the booster in place. Bigger wheels would make life a lot easier. Plus, for any kind of high speed cornering you'll almost certainly want lower profile tires that will need bigger wheels. If I get the C4 HD brakes installed I'll have two sets of 15 inch stock wheels to get rid of.

i had 12" C4 front brakes on my 71 Nova with a manual master cylinder for a 77 Chevelle, and it just flat out stopped when i wanted it to once i got the brake bias dialed in.. pedal effort was about the same as any late model car- my then 53 year old mild mannered mom drove the car a few times and didn't think the pedal required too much effort. i loved the way that car stopped, but i didn't love how some 15" wheels would fit and some wouldn't. using the C3 rotors would push the caliper farther back from the mounting face of the wheel and allow a wider choice of wheels- plus there is more beef there due to the thicker braking surface. the wildcard in my plan is the LS1 calipers- i don't know if they are bigger radially than the C4 calipers.. i guess i could use the HD C4 calipers for the 13" brakes since they just look like the regular duty C4 calipers only wider to accommodate the thicker rotor, but those cost more than the LS1 calipers.
i guess there's nothing left to do but start buying parts.. i wish i had a spare set of spindles to modify so i don't have to take my daily driver off the road..

Check out lukeskaff.com It's what I'm using as a guide. He has a mass of information on several of these swaps including which calipers/disks etc. etc. work together and with what size wheels.

i just realized today that what i'm looking to do is copy the 68-69 Camaro JL8 front brakes, except with a more modern lightweight 2 piston floating caliper instead of a cast iron non floating 4 piston caliper. those cars had 15X7 steel rally wheels on them, and pretty much every aftermarket wheel of the day that cleared factory disc brakes fit on them.