throttle servo thread
steering servo thread
I have asked questions in both these threads and it helped me choose my servo's. basically roadracer gave you a good guide to follow. 200 + torque for steering, and i would say 150 + for throttle to be safe. You can also try and go with something a little faster for the steering, say around the 0.10 to 0.12 mark.
Anyway those 2 threads will point you to all the info you need. (also try searching "servo" or "steering servo" in the nitro thread, you will find lots of useful threads).
Hopefully we dont need to have another manufacturer war here
Good Luck.