Best to see the needle barely moving as not to generate too much heat, I slowly start closing the valve when 3/4 the way there. There are in line regulators if you feel the need. Huma comes to mind.
My v1 GK1 has a larger cylinder bore, all I have shot out of mine is .22 JSB 25.xx There is a head shot pic in the head shot thread. Rocker1 .22 LDC on the end makes it back yard friendly at 45 fpe for a full mag.
Smaller target from 20 yards, GK1 JSB 33.xx pellet. This one hung around way to long, I walked 20 yards to the truck to fetch a gun and back, if there was nothing in the way I would of tried it at 40 yards ;)
I used an automotive 50/50 premix, they use purified water in the process, 50/50 as it will give me freeze protection in Wisconsin. Warmer climate the anti corrosion additives are an advantage.
I put a 18mm Buck Rail Collet Suppressor on mine. It directs air back into the shroud for more quiet. https://buck-rail.com/product/collet-suppressor/ Here it is in action.
I do not run my GK 1 at max pressure, 4000 is the max I put in it typically sits around 3000 give or take, this is my everyday carry at work for farm pest. I do have the GX 4 compressor so 5000 is possible.