GRRT prop
Running that 8x6 prop on the GRRT is like running a 5-speed car in 3rd gear. I bet you have AWESOME acceleration, but top speed isn't as high as it could be. To get the most speed out of your pylon engine on a 3 pound plane try a 7x9. That's been the best combo for my GRRT/D. Dust that I have found so far. A lot of guys will tell you the 7" prop is too small to do anything, but that is on their whiplashes; the Dust weighs quite a bit less, so less static thrust is needed to take off and fly well.
Carl