Also, why are you replacing the card, did it fail, or do you need a more powerful upgrade? Most likely, a HD7750 is a good choice. It doesn't need a PCIe power connector, so you won't need to upgrade your PSU as long as it is at least 250W. Even so, it is considerably more powerful than the HD4670.
If you need anything stronger, we'll need information about your PSU (brand and model please, not just wattage), your resolution, and your budget.