Contrary to the original posters claims, the Chinese Garrett knockoffs are close enough to Garrett originals to swap parts. You can pick up these turbos for cheap and throw a Garrett rebuild kit into it and have a really nice turbo for reasonable money.
I am thinking about picking one up just to take it apart. In theory you could use these turbos to experiment with. Play with different size compressor wheels and turbine housings to tailor your power curve. Then once you work out the combination that makes you happy, buy the real deal from Garrett.