Icing is a myth. On the road a properly set choke with high idle , the charge will not be effected. 440's have been air gaps since there were 440's. Factory 440 don't have icing problems.
Down side, you won't see much power improvement because you separated the hot oil from the runners...Hot oil still hits the base of the intake unit, and aluminum transfers heat nicely. 440's don't even have the one peice botttom, 440 have a separate pan. No oil hits there intakes.
The Performer/ and RPM air gap runners have been changed, well as plenum volume, and texture. These alterations give the fuel more volume with a straighter shot to the chamber, while maitaining mix velocity. The EPS performer , and air gap performer make about 10 more hp on a dyno . Attached or not becuase they improved the runners.