Asus gtx 560 not performing what i expected?

Hey I have a:

Model: Packard Bell iXtreme M3720
Motherboard: MCP73PVT-PM
Processor: Intel Core 2 Quad CPU Q8300 @ 2.50GHz
Ram: 4GB
Graphics Card: Asus GeForce GTX 560 810MHz
Power Supply: OCZ 500w stealthxstream

and I have just recently upgraded from an NVidia GT 240 to an Asus Gtx 560 but I haven't been getting the FPS i was expecting.

For example in games like Battlefield 3 I get about 20 - 30 fps while in middle of fights and about 35 - 50 fps when im outside of a fight or looking where there is not much happening. No matter if I change the resolution to 800 x 600 or put settings on lowest ,this fps does not change at all. I was even receiving same or slightly better fps with my gt 240 when on lowest. I also have this problem in Bad Company 2.

Another game like Team Fortress 2 & Left 4 Dead 2 is very playable and I get much over 60 fps however when I get into the action I seem to experience around 30 - 50 fps (which is quite annoying) when maxed out but without anti aliasing. Crysis 2 did not run greatly either and not brilliantly when put on high (lowest setting.) Deus Ex Human Revolution I experience low fps when many people are near and not perfect fps when nobody is near.

However other games like CSS, Payday the Heist, Magicka, Killing Floor, Flatout UC and some other games all seem to run fine. Call of duty seems to run very well but online I also experience fps drop below 50fps.

What could possibly be wrong, i was expecting 60fps+ constant especially in most of these games, especially looking at benchmarks and videos of the gtx 560. I know my processor may be bottlenecking me in intensive games like battlefield but i was expecting over 50fps even if I had to lower my graphics settings. Just asking if anyone has any solutions to the problem.

Other information are I have tried the 285.62 and 290.53 beta drivers but they didn't give me any differences. I am also using a DVI to VGA converter to connect my vga cable to the card.

I also think I might be using molex to 2 6pin connector however im not 100% sure since the store put in the card for me and when I received my box back, the cable was not there so im just assuming they are using this connector.

Any help would be greatly appreciated. Thanks :)

Thanks for the advice. I'll consider buying a dvi cable and also i found that if i set my process priority to high in bf3 my fps increases by about 10 fps which is ok. If the dvi cable doesnt help then it looks like im going to need to save up for a new processor