The Gigabyte GV-N770OC-2GD and GV-N780OC-3GD are good video cards. Their performance is in line with other GeForce GTX 770 and 780 cards, and the overclocking potential is fine. A strong side of these cards is how silent they are when idle.
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips