See this hierarchy chart:http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html
If you jump up 2 to 3 levels you will see a big increase. Befre you go out and buy a new GPU make sure of the following:
Your power supply will handle the new video card.
The new card will fit in your case
Your CPU will not bottleneck the new graphics card on games