I bet the reason you didn't get feedback was the real answer is "it depends" There are so many variables that it is impossible to give a ball park figure without someone having the virtually identical combo.
First off, how much NET valve lift do you have? Take away lash, and another .020 for flex, and you may be close to what flow the motor can access. Don't forget that the valves are not at peak lift very long, so the numbers that mean the most are below the peak. Compression increase is fairly consistant I believe, but other areas may not be.
My WAG would be based on a very well matched exhaust ,intake, carb and cam setup that is making close to max hp for the flow you had before, which should fall in the range of 2 hp per cfm. Now take a look at the AVERAGE flow increase from say .100 to max net valve lift and see what you have. You might see 2 hp per cfm gain, maybe not.
Case in point. If you had installed those heads on my old 535 cube stroker, going from the iron ported 906 s that were on it to the new ported heads would show some very serious gains in deed. The motor is choked to death by the heads. Do the same trade on a 383 with a stock cam, and you might not see any improvement.
I increased the flow on my 440-1 heads by an average of 5 percent. But I got ZERO gains. Part of the problem may be that there is a spot right in the mid lift area where the gains go down to very little. The other is the cam may not be the right grind for what I now have, or other components don't match and restrict the increase in Hp. I may not be running the motor up high enough either. Lots to think about.