Hi,
Thought you might be interested in this info. I rang GCG turbos (really friendly people and easy to talk to) to get a quote for a high flow rebuild on the RB25DET standard turbo. Here is what they told me:
They replace the standard ball bearing, replace turbine and compressor wheels with higher flowing steel items. They also machine the housings to suit. They do two different trims. Stage 1 costs $2,200 and they have been able to get 225RWKW, stage two is $2,450 and they have been able to get 257RWKW. In stage 2 trim the tuebo was running 25PSI Boost.
They also told me that Garret GT series and HKS GT series turbos are not rebuildable. The GCG rebuild retains it's rebuildable qualities and comes with a 12month warranty.