I'm looking to add a turbo to my rx7, I wanna know which ones are the best for redlining at 6000rpm? thanks. also I wanna spend about $400-$500 for it. the cheaper the better :-)

As a general rule, the bigger the turbo, the longer it takes to spool. I say go go to the junk yard and see what you find

its all in the A/R baby!