The 650W PSU should be good enough to run the R9-390 with some OC'ing if desired. So you could use either card once you get the new PSU. Both cards will do the job using one monitor for gaming and one for video work. But keep in mind, any time you try to do that kind of work in the background while gaming, both the game and the other app will suffer some performance loss. You will need a strong CPU to play an online multiplayer game while you are rendering video.