None, wait until the cryptotards cash out because coins stop being profitable. That said, I own a RX480 and it can run Beam with 60 fps plus on most maps.
I have a gtx 970 and totally recommend however you need a pretty good prossesor to compliment it and get max fps , I have a old I7 3770k and its holding me back where the gtx 970 is barely having to work
Bliddy cryptominers. All of these will run Beam well, but the 970 is aging. The RX 480 will net you the performance you want for less than a 1060, so when miners have finished killing the GPU market, buy one.
I got my GTX 1060 (6gb) literally a few weeks before stock disappeared. I can get 60fps on high (with post-fx off) with one car and 50fps once I have about 3. I am also running a i5 7500 so performance will vary.
Get a 480 8 gig. performance-wise, it is as good as/better than the 1060, but it has more VRAM and is cheaper (most of the time)
Don't worry about it. The 4GB RX 480 is still a powerful card, and you are lucky to have gotten one with all the miners around.