As you're still using Vista, DX11 isn't that useful as it's Win7 only. So I'd recommend trying to get a 4870 or 4890. Both are good value and offer good performance. If you do plan on upgrading to Win7 in the future, the 5750 is fine, so is the 5770. However, the 4890 is faster than both, and the 4870 is on par with the 5770 at the moment. That said, as always with upgrading your graphics card, make sure your computer's PSU (power supply) can support the new card. Specifically, make sure it has a PCI-E 6pin adapter, as that's what most medium-high end graphics cards need, I know the 5750 and 5770 need one. The 5750 doesn't use that much power so anything around 400-500W would be fine running it, for the 4870 and 4890 I'd think about upgrading your PSU if your PSU is rated lower than 500W. To find out what your PSU is rated at just take the side panel off and look on the side of the PSU, there should be a sticker with some info on it.