Some rambling thoughts-
IMO piston coolers are more important if you run high EGT's and for long duration.
My NHC250 with a N16 turbo makes 18 psi at 2100 (20 button and 225 psi fuel rail). I have no intercooler so my charge temp is higher than a nat aspired version (maybe 220*F max). I have run WOT for long duration, on a 90*F day (high ambient), pulling a 30,000 lb trailer (Stalwart and 11 ton equipment trailer)... my EGT's have never gone above 700.F (probe after turbo). Not once. 600-650 is typical. This includes running at lower rpm's, which tend to make the highest EGT's. That is because when my boost drops so does air volume, that extra air being really good for cooling EGT's, and pistons.
As for adding 50 or 100hp to a stock NHC250, well, I think squirters are over rated. If you want 500HP and plan to have a 20 something kid haul freight cross county, Ok, go get 'em.
If you think you need squirters you might want to go for some steel piston crowns too. Some of the big rigs I used to drive had them. and while we really beat the crap out of them they rarely ran high EGT's.
Oh, btw, hot street cars can, and do, run higher EGT's than diesels, 200* higher. Few have piston squirters. To be fair they run higher rpm and that throws more oil around. They also run WOT for short duration, lasting only a few seconds. But what we are talking about is thermal control, and those do get hot.
High performance marine see long duration. A pal professionally build marine engines. Supercharge stuff in the 600-900 HP range. I have looked them over on occasion. They look like HO auto to me. Squirters? I doubt it. Next time I see him I'll inquire as to special piston cooling requirements for them.
Top fuel drag race engine? No squirters too, well, I assume. But then they only have to rotate 540 times in anger. if anything is left they come apart, get patched up, back to work...Amazingly, the mechanics never seem to complain. Maybe they do when no one is watching.
Anyone here with a big diesel tug boat? Please let us know how oily your pistons are.