What PC part to get next?

I just got a new Radeon sapphire r9 270 and I have 500hdd, 4gb ram, Intel i7 860 2.8 ghz and an old ugly green and orange biostar motherboard. I play games like battlefield 3,4, h, minecraft, csgo, mortal kombat X, fine at 60 frames but some other games just don't meet my expectations. I really need a new case motherboard and processor because there's a stripped screw in the mother board so I'll have to get all of those, or if I should just get more ram or like an sli gpu. I have a 750w psu so sli would be fine. Just can't. Decide