Re:how much more oil...for turbo?
 

guess what, I've used -4 and -3 without problems. I prefer -3 because its smaller, easier to work with, looks better and the ID of the -3 is about the same size as most factory turbo charged cars oil lines.

Re:how much more oil...for turbo?
 

Aside from physically measuring the oil feed pressure on an OEM, matching ID with an OEM would get you close enough. I personally set mine with a T-valve to not exceed 40psi at high revs, but still register at idle.

Re:how much more oil...for turbo?
 

My kits come with a -4. I doubt you would see any different pressures from either of the two. Flow, maybe, but not pressure.