hi im in middle of building 500+hp cossie engine but cant decide on what turbo to go for ... or which ones going to be the best option in the long runfor reliability and performance

some of the parts so far -

4x4 engine with ported head, double valve springs and bd15's.
low comp .5 oversize pistons with valve cut outs and standard rods.
ill be useing omex 710 management as well, siemans 83lb injectors and swedish type inlet.

im hearing so much talk about the gtx and the BW i just dont no ...
im hoping some of you guys would be able to help out with some advise
this is going in my 2 wd sapph and will be used as my 2nd car ( for road and maybe some track days , santa pod etc).

cheers