Before the ban Porsche Dude posted a link to a site that sold a lot of the GT non-ball-bearing stuff at reasonable prices. It's the fancy-schmancy ball bearing stuff that's expensive, the conventional bearing turbos with GT wheels weren't all that much more than old school garrett stuff. And the wheels are better, I've seen several tests that have convinced me of that.

For any straightline car I don't think I would bother with the ball bearing, I shift at WOT with a clutch cut and if the car still loses too much boost I'll throw in some timing retard on shifts to help out or work on banging those gears a bit faster. For a car I'd use on a track with turns, I think the ball bearing turbo would shine if I was running a turbo at the upper limits of sizing for the engine setup and was demanding fast transitions into boost at lower rpm above the spool threshold. With a properly sized (reasonably sized) turbo and a good 4k range of power I don't think it would ever be an issue.