Of those options the 460 is probably the best. The Crysis series, BF3, Witcher 2, Metro 2033 and Arkham City can be quite demanding, even at low resolutions. Crysis, Witcher, and Metro are demanding because they really push the limits of graphics technology, even the 6770 will struggle with them if you crank everything up at 720p, Arkham City is demanding because it is a horribly coded mess in DX11 mode, DX9 mode is considerably easier to run though.
What sort of power supply do you have? The 460 uses the most power out of all those options, you may need to upgrade your PSU if you don't have a good quality 450 Watt or better power supply.
It has the best chance of doing it out of the cards you listed, though you probably won't be able to max out Crysis 2 and Metro 2033 and maintain an acceptable framerate. Those 2 games almost need either a top of the line card or a dual GPU setup to max them out on just about any resolution. Arkham City you'll probably want to run in DX9 mode until rocksteady finally gets around to fixing DX11, they've been too busy counting money to be bothered to fix the horrible PC release. Original Crysis, BF3 and Witcher 2 should be fine, though don't turn on Ubersampling in Witcher 2, that option absolutely slaughters your framerate if you don't have a ridiculously high end dual GPU setup.
Your PSU is plenty for a 460 so you don't need to worry about that. If you are dead set on maxing out Crysis 2 or Metro 2033, you may want to aim for a higher card, but that would largely be contingent on if you have $200+ to spend.
You should be able to play Metro 2033 on high (Medium recommened) and get maybe a 40 fps. with the GTX 460 thats your best chance. Believe me, i can't even max the game out and i have two 560 ti's . But far as the difference between Medium and High isnt much in Metro. BF3 and Crysis (1 or 2???) you can do about the same. I know people that can play it n high with a 460 at 1080p
Damn....so even on 720p, 1.5GB Vram is need for Ultra in games like Bf3, that really sucks
So even the GTX 560 and GTX 560TI can't do it at that res
Can anyone point me to a Vid that Shows BF3 Truly Maxed Out
At 720p you shouldn't need more than 1GB to max out any game current game (aside from Grand Theft Auto IV, but there aren't any other games out right now that use as much VRAM is GTA IV), even BF3. Having more than 1GB only really helps if you are running at 1080p or higher, and doesn't really become essential until you get to ultra high resolution displays and multi-monitor configurations. At your resolution a 6870 or 560 with 1GB should be enough to run BF3 on ultra. You may not necessarily get a solid 60FPS, but you will certainly get playable framerates.