Throttle curves and my opinion. I've tried total linear throttle curves and they really don't work for me. Forget about RPM's. They work so much different in the air depending on props etc. Fly the airplane and see where you feel comfortable for cruise speed. While your doing that, look, or have someone look at where the stick is. Make a note. Now, when you get it on the ground, go ahead and tach it where your stick was. Use that RPM reading for your center throttle stick position. Then start working on your curves above and below this point where you feel comfortable with it. If you're into 3D, do the same thing.. where YOU feel comfortable to have that center stick position.

I'm sure there are people who have different ideas, but I like to have the throttle center in a position where I can work up or down from there, but most of the flying done is at that position.