assuming both intake and exhaust cams on an otherwise stock FS, something like 5-7whp...
So nothing major, but they do significantly change the curve, and make the engine breathe noticeably better at high rpm...so even if the recorded gains are mild, it does make the engine more fun to rev...if that makes any sense...
I bought a set from corksport back in like 2003 and installed them at the time on an otherwise completely stock FS...it was the very first performance mod I did, as I HATED the way the FS just face plants at 6000rpm...with them the engine cleanly pulls to redline and a few hundred rpm over...definitely worth it because of that for me at least...
still use that engine when not using the built FS, and have nearly 130,000 miles (about 100,000 of which have been with those cams)...no mechanical problems...
just a note: if you install these yourself...no matter what...replace the timing belt tensioner (and the belt itself if you haven't in a while, you have to remove it anyway)...just the process of loosening and re-tightening it will drastically reduce its life span...i've slipped so many of those I don't even want to talk about it...just use a brand new one...