The 422 I built some years ago runs 596s I gave a Stage II porting to. they run a 2.05/1.65 valve package. They were never flowed but I guessed around 240-250 @ .500. The engine makes close to 470hp based on MPH and weight. The cam it uses is an older Crane hydraulic, with .490/.500 at the valve and around 240° @ .050. The key is low lift flow, and that's where the larger valves will help with very little other work done. I agree the gain by just addding 2.02s and a 3 angle stone valve job is minimal - I'll bet noone posting here could feel the difference in a driving car myself included - but when it's coupled with a high quality 5 angle valve job that provides a very good approach to the seat (never mind the blending or laying back the short turn) it will make a measurable difference. If you're not going to optimize the work and quality, the results will never be optimal.
I'll add - the 596 heads as cast are not enough to feed a hungry 4" stroke engine. It's not displacement - but stroke. You increase the stroke by 18%, so you need 18% more air with no other changes to maintain the same type of power curve. Without providing more air in the volume you need, you will end up with a very torquey engine with no lungs to rev. Big torque, but a steep drop in power after the torque peak. For some that's not a problem, for others it is. I'd expect it to make decent torque right off idle, and have a horsepower peak around 5-5200 depending on the cam, and after that, it will fall off fast.