Need help choosing a graphics card

[Shintrasix]

So, I need help finding a graphics card that can run Battlefield 3 on low or even medium settings easily.
I don't know much about the topic at hand so I'm hoping to get some helpful straight-forward answers.

These are my PC specs:

Processor: AMD Athlon(tm) II X4 630 Processor 2.80 GHz

RAM: 6.00 GB

Graphics card: ATI Radeon HD 5450

Power supply: 460w total

So preferably I'd like a card compatible with what I already have without having to increase the power supply etc.
I've posted threads similar to this one on other forums not strictly about computers but most of the responses just directed me here.

Note: I'm not at all familiar with this website or the forums here so I apologize if I posted in the wrong area.

 

[hameem 1]

i think the HD 6770 is your best choice for 460w

 

[Shintrasix]

Thanks, as I said above I've asked this question before and most people have suggested a 6870.
I'm pretty sure I'd have to upgrade my power supply for the 6870 not to mention it would probably create a pretty noticeable bottleneck.