The set up I've been using for the last year which works great and it reasonably priced is: Himax 2015-4100 motor, GWS EPS gearbox with "D" gearing, Castle Creations Phoenix 25 amp ESC and a 3s 1200 mAh lipoly pack of good quality such as an E-tech or Thunderpower.
This set up performs perfect in a foamy of the size that 3D Foamy sells. Plenty of power and it won't break the bank. Sure you will net a little more power with a Razor or Hacker but you'll pay twice the cost of a Himax to get it.
I hope this helps but one thing's for sure, you can't do any better than choosing 3D Foamy for a flat plane.