There are some pretty dedicated threads on RCU about both - generally in the 3D forum. Look for the one on the QQ yak started by Aerobob - he did a build on that one with the Brillelli 40. Per Brillelli the 46 is more powerful, but only about 3-4 ounces more with the new muffler on it. Bob even has some video posted so you can see how the engine pulls the plane. Although he has a dead-stick that turns into a dead-yak.