That’s a lot for a gtx3076r I could probably get you a better price than that.
As to which turbo is better tough to say most DSM dummies run these at like 35-40lbs where the gtx’s shine actually. But even if you were running 35psi+ the GT3582r still flows similar to the gtx3076r and outflows it at all boost levels below it. The gt35r flows up to 68 lb/min, while the gtx3076r only flows 64 lb/min and must be at 30-40lbs to achieve this. The gt35r can flow 64+lb/min from 20lbs and up to 40lbs. The gtx3076r might get you where you want to be but its tough to say. As a sale person I always like to guarantee results so the gt3582r is a safer bet. On my own personal cars would I try to get to 600whp on a gtx3076r you’re damn right hell I made 574whp on a gt3076r. 600whp can’t be assured on either turbo if the motor is inefficient though. So I would expect a proper manifold not cast, good flowing head and cams, etc.
Another turbo to consider would be the gtx3576r. GT35r turbine wheel and gtx3076r compressor wheel. This one would be quite a bit more money though.
Dont worry about trims or a/r, trim is relative to the size of the turbo so larger trim doesn’t mean larger turbo. A/R also is relative and these housings can be swapped for larger ones anyway.