It seems to be most common for people to replace them after 600 RWHP. I don't know if they are being exceeded before then, but 600 seems to be the most common time to switch out. Our fuel rails are pretty big....
I've got Mallory fuel rails and no where near 600hp. I switched because I bent one of the stock ones pretty bad pulling my motor out of the car, so I figured I might as well upgrade them. The Mallory rails are huge.
well im looking at about 450-500 horse at the flywheel so it sounds to me like ill keep the stock ones. i will also be getting a large fuel pump. i already know about that.