||I know of a guy in the UK (where i am from) that has done an insane build. Upgraded everything possible, shipped his engine over to EPR racing in the US, got solid tomei lifters etc etc you name it hes done it obviously spent an absolute fortune and still using GT525's.
It absolutely baffled me seeing he has done all this crazy stuff like modifying the oil pump, getting a huge spec set of heads and all but kept 4 bolt turbos, they must be good I guess.
I'm planning a turbo upgrade soon but i'm going to go for gen 2 2860's, i'd rather have ball bearing turbos that JB's but each to their own
You can see his 25 page build thread here if your interested