RE: Saito 120 & 150 rpm
This is what I've seen:
Saito 120 w/ APC 16x4W on 20/20 fuel = 10000 rpm
Saito 150 w/ APC 16x8 on 15% Omega fuel = 9000 rpm
Saito 120 should get 9300 on APC 16x6, while Saito 150 should get 9700 on APC 16x6, both using 20/20 fuel. I think 16x6 is too small for Saito 150 to show its advantage.
On a 4.4 kg plane, you are better off with Saito 150 and APC 17x6 propeller, swinging at about 9200 rpm. This will generate about 15 lb. of thrust.