There are a ton of brake threads, but a front only big brake upgrade will be a decent improvement. I went with Stoptech on my Viper and the braking is much better, especially at speeds over 100 mph. Track performance is quite good and it is easier to threshold brake.
These brakes are still not up to Porsche Turbo standards, but are quite an improvement for $2500. I've run with a few 996TTs at track days and the cars seem pretty competitive overall, but then it was just for fun, not a race.
If I wanted to spend $100,000 on one car, a used 996TT would be on my list, but so would an F355 (I ended up buying a Viper and a Z06)
Also, Porsche is coming out with a street version of the GT3 which looks to be awesome. I'd rather have the GT3 then a turbo.
Jim