I personally would go no bigger than a Garrett gt/gtx3076r. Depending on your power goals top mount, low mount factory manifold ect. For top mount I think a gt3076r would be ok. For factory manifold its hard to go past a hks 2530/2535/2540. Although some would argue the hks 2540 is a extremely mismatched piece of . I'd go a 2535 exhaust, cooler, injectors, decent ecu and clutch and save for a rb25det conversion. A rb20 in miles behind a rb25 in so many ways as status and others have mentioned.
Cheers Josh