Problem is they cant keep in chape during high power and high acceleration they will start to vibbrate and saound realy bad.

Here you have some messurments i have done on the Actro motors: http://web.telia.com/~u15807174/TestmotorerActro.htm

The 20x10 has abit to much pich for good 3D 19x8 or 20x8 is better i think.