for a 500+whp setup that will see street time, I definitely recommend the S300SX 83-75. The ideal A/R depends on the boost level you intend to run. For under 22/23psi, i recommend the .91 a/r. For up to 30psi, use the 1.00 a/r. The housings both spool very similarly, but the .91 has a little bit of a response advantage over the 1.00.
which header do you intend to use? I rarely recommend the ebay divided manifodls becuase they are total junk 99% of the time, but i recently saw a friends 7m ebay manifold and it was divided and i am surprised to say this but i would recommend that manifold over anything else ive seen for the 7m. its divided, cheap and moderately strong. not great materials and not great welds, but the 7m i saw had better welds than any of the 2jz or honda units ive seen in the past.
i hope this helps
-geoff