You might be able to *just* get away with a GeForce GTX 650ti, though it may bottleneck it a bit due to your PSU, the card itself will use 110w, but it's not that expensive to upgrade to a 400w PSU (I would recommend Corsair if you choose to). I would say it depends on how much your other components are using, I mean a recommended specification isn't necessarily the least you'll get away with. I did run my GTX770 on a 550w PSU (spec prefers 600w) and it was a little bottlenecked, I got away with it because my other components weren't using a lot of juice, but when I upgraded to 750w, the performance increase and temperature decrease was pretty nice.
If you're worried about it and can't upgrade your PSU, then the GT 640GDDR5 is the prolly the highest GeForce for your PSU (the non GDDR5 one requires 350w, so in this case, the better of the two cards requires fewer watts).
But the reason why I would recommend a GTX650ti:
You get a lot for what you pay for. I found despite it being inexpensive, it gave me a lot of power. I had no trouble running any modern games, granted for the highest end stuff I would adjust the settings slightly (like turn TresFX off on Tomb Raider).
This is a video of me running Tomb Raider my old GTX650ti
Of course, your other specs will let you down a bit, but it's a good card. I say a shame that mine died on me - it doesn't put me off of the card, I used a manufacturer I never heard of and to be fair, all manufacturers have a failure rate and sometimes you're unlucky. I *could* have claimed under warranty, but Amazon had such a good price on the 770 that I couldn't say no.
I don't know what the GT640GDDR5 is like, but the fact that it has DDR5 is in itself quite neat and offers nice clock speeds as a result...considering it's not really on the higher end of spectrum.
If it helps, this is the card running Battlefield 4
With ATI/AMD, I've not gone with them for quite a few years now, so I can't really offer any kind of fair comment on them, I just know that spec for spec they're the cheaper...at least on average.