RE: TWIN FEVER !!!
I built about as streamlined a plane for the .074 as you could get, put a oversized venturi on it and ran it on bladder. I tried every prop from 4.5x4.75 on up and couldn't get much speed out of it, but was able to kill overall flyability very well. Unless you were to grind the case down and get the engine really singin' with some mods, speed with .074s is kicking a dead horse. I have a few .061 powered planes ready to scramble when a serious .074 powered job comes a callin'!
By the time I found a prop small enough to allow the .074 to get into a happy zone, it might as well have been put on a smaller and lighter .061 in a smaller plane. The power / drag / speed formula favors less drag over more power by a factor of 3.