If the TEV is rated for 1 ton Nominal, can it be used for 3/4 to 1 ton systems?

The a/c's I want to experiment with are usually 8500 btu and 9600 btu.

My goal is to have an a/c that puts out a constant evaporator temperature, preferably 35F, but no higher than 40F.

The cap tube system that they currently employ varies in temperature from 40F to 55F.

I even thought of trying R408A to see if I could maintain the desired temperature. I was told that R408A is not as efficient as R22.

What is more efficient than R22?
R502? R407B/C?