You won't gain any power with the FPR.
The FPR will let you add more fuel when you get into a lean situation on the top end after a bunch of mods. You can safely get 20-30% more out of your injectors. If you turn your fuel pressure up too high, the injectors will drip which really screw up your idle. (There is soo much pressure that they can't stay closed.)
You can make your stock 16lb/hr injectors work like 21lb/hr injectors. Check out
this page to see what I mean.
HTH,
BP