The hd4870 supports DX10.1 it does not support DX11. The DX11 is not crucial for win7 but the general consensus is that it is nice to have for the games that support it. At this moment there are only two games out that support DX11.
So HD4870 is going to work fine with Windows 7 and is the most powerful card you listed. The HD5750 is the only card that supports DX11 that you listed, for a little more ($25) you can get HD5770 with DX11 support and similar performance as the HD4870