Yes if thats the case then upgrading the video card will be your best option. If you have spare molex connectors on your psu, you could always buy a PCI-E power adapter so you can have two PCI-E power cables to give you more choice.
GTX 550, ATI 5770, ATI 5850
Look here for hierarchy chart on GPUS http://www.tomshardware.com/reviews/gaming-graphics-card-radeon-hd-6870-geforce-gtx-570,2834-7.html
Obviously you cant go over the top on the GPU such as a 6970 because you will require other upgrades.