I'd say a lot. Having owned a '85 5.0 LX with a 5 spd and 2.73 gears, I'll tell you that car was an animal! And it was stock, save for the '87 factory dual exhaust I put on.
My advice: If you're tinking about going to a roller cam and you haven't bought anything yet, buy a late model rollerblock! it'll be cheaper in the long run. Use a 28 oz 302 crank with the ring ground off to fit in the late model block and keep the 28 oz balancing to re-use yor flywhell and damper.