I can't remember where I read it (so treat this as a rumor:) ), but the HP difference between the RPM and RPM Airgap was only around 5 HP. Not enough to make a significant difference.
150.00 is a good price, but not a great price. A new Air Gap can be found on ebay for 168.00, with free shipping, is 5 HP worth $18.00?
I would think thats a rumor, 5 hp is a lot, unless maybe they were running manifold heat into the rpm which would kind of make me wonder why use a Hi Performance aluminum intake in the first place?