I have a Park 480 1320Kv (http://www.hobbyking.com/hobbyking/s...r_1320kv_.html
) with 45 Amp ESC in my 350. C of G is fine with this motor and it flies well.
I fly off grass in a park and I have not needed to change from the stock wheels.
Best C of G on the 400 is 60mm from the leading Edge of the wing. The 400 you will need two servos and a reverser if you want to use the flaps, the 350 has working flaps out of the box.
Both can be difficult to see against white clouds.
I hope this info helps.