I've heard there's issus with the build quality of the RM series. Not sure if they fixed it yet though. Not terrible quality, but not the best. A good 650W will do for any single GPU system, and 850W is a good number for a dual GPU system.
You'll want XFX, SeaSonic, EVGA (some of them), Antec HCG, or Corsair AX/HX/TX.
https://community.newegg.com/eggxpert/computer_hardware/f/135081/t/45344.aspx?Redirected=true
You can also consult that list. You'll see the RM750 is a Tier 3 PSU.