Finally broke down and bought an air-gap

Air-gap is great as long as you do not live in a cooler climate (okay cold) - or expect min. 10 minute warmup - and maybe longer. In the hotter locations (like Henderson NV) I doubt that is a problem.
I had a LD340 on my 388 and thought it was starving at the top end, so i switched to an Air-gap - and had no noticeable difference IMO. For mainly street use with a bit of strip I would go with the RPM performer.