guanyu210379 :
gtx770 and R9 280x are almost the same in term of performance but GTX770 is slightly better.
For both, I think you might need to upgrade the 525W PSU too.
It depends what the PSU is, Sirdanial99 could you give specifics on the PSU- make, model and most importantly what 12V rails it has (i.e. if its 1 x 12V @ 36A, or 2 x 12V @ 18A etc).
[strike]Also- there is little point upgrading to a 770 or R9 280X from a HD 7950. The R9 280X is based on the same Tahiti GPU as the 280X, and the GTX 770 is based on last years GTX 680 kepler GPU which was in a similar ballpark performance wise to the HD7970 (ok both updated models are clocked a little higher, I just don't think the step up is enough).[/strike]
Ah I can't read! A GTX 770 or R9 280X are both a good step up from a 7850 sorry I misread that! I would say however that your rig should cope with those games fine (you may need to turn the eye candy down a notch).
If you're going to upgrade the GPU then you need to be shooting for either a GTX780 or 780ti (don't bother with Titan its more aimed at compute work than gaming) or the R9 290 / 290X (avoid the reffernece card, the ones with custom coolers are much better).
I don't see your rig really struggling much with any of those games you've listed though at the moment. The best upgrade you could do right now as previously mentioned would be an SSD (note this won't improve frame rates in games, however it really speed up boot up time as well as game loading and so on, and price on SSDs are getting much better now).
If you don't fancy that then I'd recommend waiting for now- Nvidia has a new range of cards due out soon (they have already released the new mid range 750 / 750ti and although not particularly fast its very efficient- so I imagine the higher end models will be good), AMD will probably launch new cards a few months after Nvidia (so I'm guessing towards the end of the year) most of the current 'new' cards from AMD are just re brands of the HD 7XXX range (the only real new cards were the low end R7 240 and 250, the 260X and the R9 290 cards).