This is going back 25 yrs (testing my memory here) but I ran Stage V's on my 500 inch 440 in a chassis car at 2400Lbs with a Glide. I spent all my money on the short block and had to scrimp on the heads (there weren't many options anyway back then). I believe with just a gentle port opening and some bowl work we got them flowing in the 280-285 range. I did use a Crane offset intake rocker and 2.14/1.81 valves.
The difference on the V over the IV in addition to the better exhaust port already mentioned was the oil passage was smaller dia so the pushrod was able to move over a little if I recall correctly.

It was a great combo, it would run 9.50's/9.60's at 140 with a 1.28 60 ft. Through the years I have seen guys with better heads not go any faster. I think the port velocity must have been way up there and it just plain worked.