Been there, doing that..
Start with an HH pad upgrade first and stainless lines and make sure you break them in properly. This is the minimal cost option, if that isn't enough for you (for 90% of people it is)...
Go to SVRider.com and Blair from SV raceshop makes a GSXR caliper adapter so you can mount GSXR four pots or six pots to the front. Six pots are all for show and have proven to not have the same pinch that the four pots do, that and bleeding them can be a bitch. But if you like the bling....
I've been running the four pots for two years now with very few complaints, here are some caveats:
-You have to buy a pair of adapters. Sell the other side on the GS500 boards with your other caliper that you won't use to recoup your loss.
-You usually can only buy a pair of GSXR 750 calipers. See above.
-You can use your existing master cylinder but I would recommend upgrading to a stainless line for better feel. These brakes have much more grab and power than the two pots (stock). You can use the stock rotor as well, just be advised to keep a closer eye on it because the more aggressive setup will wear it faster.
-No, it's not as good as a twin caliper/rotor setup but is 100% less of a PIA than doing one as well. It's pretty damn good though and I can late brake with the best of them. Would double disc be better? Yes, but this is significantly easier.
-With the improved brakes, you will figure out the stock suspension sucks, like really sucks. Yup, it's a gateway drug to modding the bike further, might as well sack up and budget money for a new shock, emulators, springs, oil and seals while you're at it...
All in all, a worthwhile mod IMO. Depending on how much you pay, it can get spendy. I know the brackets cost me about $100 and calipers close to the same but like I said, you can offset the cost by selling the other side to some GS500 homies. Certainly has more power and feel but take your time centering up the caliper over the rotor to avoid drag. I used some stainless washers I had from another project. Glad I bought this stuff when I had a little more money than now (which is very little!).
No problems on the one track day I did last year. Had consistent feel and power and no issues braking from 100+ lap after lap. Stoppie capable and great modulation, I used up the stock Suzuki HH pads that came with them and am now running EBC HH. The EBCs are a little more wooden but have more bite so take that with a grain of salt.
-Randy