It's acctually the equivelant of the RPM....I had ported GT-40 heads on and a B-cam, TB etc. (same as you) and when I put on the intake I picked up 2-3 mph
Mine really woke up with it, and I still have stock heads. It's totally ported, polished and port matched, but I can't complain since it only has an aftermarket cam to work with. Big difference. 226,000+ miles on the original motor too!