I think the problem is that some people upgrade their turbo on only a half assed job. What I mean is they upgrade their turbo when they are only pushing ~175rwkw from an RB25DET when their is much more left before a larger turbo is needed. I've read many threads over the last 1-2yrs on here about people with aftermarket $2,000+ HKS turbo's only pushing 210-225rwkw on an RB25DET, that to me is an absolute waste of money, better off spending it on women. They are using an SAFC instead of PowerFC, no exhaust cam gear or cams, still on the std front/dump pipe etc etc and are complaining that a $2-3k turbo upgrade only bumped them to 220rwkw.
If im going to fit an aftermarket turbo I want 50rwkw alone just from that turbo otherwise it's simply not worth it (cost vs power).
I think if you aren't making up around 185-190rwkw on the standard turbo you simply aren't trying hard enough