Hell......I broke 400 with an air filter and a superchips program.
The stock clutch is actually pretty strong.
Lots of KB car out there with stock clutches and no issues.
I still remember the days of the Jim Wolf clutches in 300zxTT's.....now THAT was a clutch!
Still.....Ford put a pretty solid clutch in the 03 and I wouldn't upgrade it until you break it =o)