Dual 270Xs or single 280Xs?

Ok so my build has a 8350, CM Hyper 212 Evo, 1TB WD HDD, 120GB Kingston Hyper 3k SSD, 8GB of 1600MHz Corsair Vengeance RAM, and a Corsair 650W CX Enthusiast 80+ Bronze PSU. Would 2 270Xs in Crossfire ($440) be better than a single 280X ($450)? And with the dual 270Xs, will I be able to OC my 8350 and both cards?

The 2 270x's will definitely have much better performance, but crossfire has more issues compared to a single card. I would rather have 1 better card than 2 lesser cards because of the future-proofability (you can add another 280x in later) and less potential problems like screen tearing. 

With just the 280x, OC as much as you like. Idk about with the 2 270x's though, it could be too much for the 650w psu, but I'm no professional. 

Both good options. Good luck.

Thanks, but, I've heard about screen tearing, but what exactly is it?

Definitely 280x. Avoid crossfire because in some games its worse than a single card.

Explanation of screen tearing: click

Some random video showing screen tearing.

www.youtube.com/watch?v=jVAFuUAKPMc

im also not a fan of dual gpu setup´s the reason it uses more power, so you need a decent psu to power it, second, if you play games that have a good optimization for it, sure the 270X CF will do better, but there are also alot of games with bad optimization, and those gonne be a pain in the ass.

summary: cf configs aren't the best, they use more power, more noise, more heat. If the game was scaled perfectly, the r9 270x will proform quite better. but if the game wasn't scaled so good (cough cough 60% of all games) then the proformance will be similar, ~5% difference give or take. If you CAN get a r9 280x, get it. if you really want that cf 270x, you can go. make sure your mobo and your psu is good.

yeah good point, you need a 990FX chipsetboard with 40 pci-e lanes, to run a 16X CF.