Originally Posted by slipstick
It's the prop size that's critical because it's the prop that creates the thrust. There are formulae available but they're quite complex involving motor losses, propeller efficiency etc so to get a good estimate of the thrust available most of us simply use one of the many motor calculator programs available, some online some not, some free, some not. See http://www.rcgroups.com/forums/showthread.php?t=606703
for a comprehensive listing of them.
Since you're attempting to fly a model with practically zero forward speed, seems you'd need a motor with low KV, low RPM and a large diameter prop for maximum thrust. Something like the rotor of a helicopter.