I wish I could find the thread where Pe Reivers (I think) talked about it, and gave actual dimensions of things... but it must be on the old RCO or already purged from Google. If I remember it correctly, the Q500 carb provides a bit more intake area than the GRRT actually needs. Having an opening bigger than needed doesn't add anything to the power output. The engine will only draw as much air as it will, even if the venturi is a foot in diameter.

I agree with ChuckAuger, whatever small amount may or may not be lost by going to the R/C carb is made up for in spades if you desire control over the throttle. If you decide you don't, then you can always use fuel tank size (or how much you put in it) to limit the length of the flight. The GRRT sucks fuel like nothing I'd seen before in a 40-46 engine. The 6oz tank recommended for the Dust only lasts for 2.0-2.5 minutes of full-throttle flight. That's a lot of glow-puke.