2 inch is about 50 mm, and 3 inch is about 76 mm. there is a good selection of very efficient fans in these ranges. i fly some 450-500 gram stuff on 50 mm XRP fans with 2 cell lipo. as do many others. take a look at the micro edf jets and power systems, and scratch built edf sections of the forums over at the groups for a lot more info.

mongo