Here's a comparison between the GT440 (Couldn't find GT430, which would be less powerful) and HD 3870. The 3870 is the slight winner over the GT440 and would really show a difference against a GT430. Also, the GT430 doesn't have enough power to actually play DX11 games well, so support is irrelevant.
Same number of steam processors, but higher clocks and double the memory bandwidth. Besides the tessellation engine on the HD 5000 series isn't very good, so DX11 isn't as big a deal as the 4890 will outperform the 5770 by a decent margin, more so at increased resolutions or higher AA.