XFX R9 280 (non X)

i wonder if that card is good at running on ultra settings on 2K resolution between 60-100FPS? I know the card is clockable to push more frames but that's where the 280x comes in. Should i get the 280x for 2K gaming or 280 is fine and is able to save me money? I need opinions before I buy one of those two cards. 

Depends on the game. I played BioShock infinite on a 1080p (basically a 2k) at ultra settings on a 7950 (the same card as the 280) and it ran at 40-50fps most of the time. A 280x is then equiv to the 7970.

You'd be struggling to get more than 60 frames per second with a 280X at 2048 x 1152 resolution on ultra settings for new games, let alone a 280. Overclocking is not going to improve performance that much.

If you want to achieve close to 100 FPS I think a 290 would be more appropriate.

Well there is definitely a difference between the 280 and 280x besides clock speeds. The 280x has an extra 256 stream processors over the 280 which is definitely a difference. That should amount to 3-6fps in most games. Not the difference between the 280x, 280 and 290 is a lot bigger. Truly the 290 is the only one in the bunch who'd be able to give the fps numbers your wanting. But the 280 and 280x have a chance to at slightly lower settings/   

290 would be a good choice. if you want to keep it on one single card.

otherwise a 280 crossfire could also be something to concider, since you play higher res, the scaling would be better, then it would be at 1080p, however, im personaly not realy a big  fan of dual gpu setups. cause it uses more power, so you need a more powerfull psu, if you dont have one. Also some games, will work great, other gonne be a pain in the ass. that depends on the game in self.