Both those cards are some of the best in their category. If your system can run the 7770, that's the one you want because it's faster. If you have a slow system or a small case or an under 300 watt power supply, then you want the 7750. You can get the 7750 in a SFF form that will fit even small cases, you can also run that card on a good 240 watt power supply.