Low FPS in 5850

I am new to the PC world (Mac guy) and have been working on a Dell I bought, an XPS 8300. It has an i7 3.4 ghz processor, 6 gigs of ddr3 ram, I upgraded the video card to the saphire 5850 1 gig ddr5 and the power supply to an OCZ 700 w modxtreme power supply.

The purpose of this computer is to explore the whole building, upgrading at PC, this is my small step in, which is why I bought a dell rather then start from scratch. Also some gaming, using secondlife primarily, as well as going to be trying WOW and games like crysis. I read good reviews on the card, so I purchased one and installed it along with the new power supply. Tight fit, but got it all in in the end. The FPS is, well, not that much of an increase over the 5670 I had in there. With the 5670 I was getting in 20+ fps. With the 5850 I am getting maybe 30, but usually hovering top end of the 20 fps. I was expecting to be up in the 50's or higher. The drivers are all updated, everything is updated. This is running on Windows 7 home premium. Is there settings or something I should be adjusting to get better results out of this card?