Just got my second Halo via trade for my V3 and I am pretty sure that I will be using the 2.5 for grey wash and the 4 mm for everything else... if the 2.5 is not what I want I will stick to the 3.2 stroke wheel..
Did a koi fish bng piece with it last week and worked great... i did like 4-5 passes on the water waves and the thing is already healed lol ... so much less trauma.

I always start out around 7 volts and run it soft with firm pressure and adjust from there... and when I find the vibration i want then I add some give if I need to.... give is not really to important with rotary