I didn't have to change anything other than adjust velocity normally to get my ghost running at a comfy 650psi. Setup is with ninja 850 output tank and sidewinder set to about 675psi. I find it's a good idea to keep output of my inline/secondary reg about 200psi lower than its input. then again, a ghost is not a phantom, so not sure how much this will help.
on my hpa run phantom I have basically the same setup, but clipped (1 coil) blue valve spring and green mainspring and run it off a stab at about 675-700psi. seems to like reg'd co2 better than hpa, but hpa is just so much more cost efficient atm. the only really noticable diff from stock was a five shots or so increase in efficiency and better consistency (well, better in that it's more consistence further into the 12g, which would only make sense... not really a difference consistency wise until the 15-20th shot into the 12g).