I’m leaning really towards going the G series route. Their efficiency over the gtx line is incredible. Fullrace can get me the g25-660 .92 ar in a t3 or I can get a guy locally to re do my manifold adapter to a v band and grab a g30-660. So many damn options lol.The only issue that fullrace said with the G series is the limited ar housings. I don’t really want to have to buy a new manifold right now but who knows lol. As for the EFR turbos, they seem to be super popular right now. Can you buy a block off plate for the boost solenoid? Also just from some light reading, it seems that people have been saying the gtx3576 is a more efficient turbo and might be a better route than the gtx 3076
That is the only real issue with the G series turbos but if you only want 500-550 it really shouldn't stop you from achieving your goals. As for the EFR turbos you can block off the blow off valve and run them externally gated.
I run a GTX3076R on my STI and make 28 psi and 475whp by 4300 RPM and it holds all the way to 7500 RPM. It's a great little turbo and I usually see them top out around 550whp on ethanol. I don't have any firsthand experience with the GTX35 as it always seemed to big for my applications as I don't care for high dyno numbers as much as I do responsiveness.