For 1080p the RX 470 4gb is a pretty good deal. I don't see much point in spending more for an 8gb version of that card. Chances are anything you'd need 8gb vram for you also need something more poweful than an RX 470 for too.
Specs are Motherboard: msi B75A-G43 RAM: ddr3 16 gb CPU: intel i7-3770T 2.5 Ghz, old gpu was msi r9 380 4g but that broke down and power supply is at the moment 500w plan to buy 650w and monitor is Benq XL2411 144hz