PSU holding back frames?

[BigBoss1911]

I recently upgraded to a Radeon 6870 1GB, However its not running nearly as well as it should. Battlefield 3 struggles to stay above 35 frames most of the time on High settings. Fallout 3 maxed out dips into the 20s when Im looking at few buildings or theres alot of people. Metro 2033 also struggles to stay above 35 frames on High settings, not to mention on I have AA turned off. I have to think its my PSU which is a Thermaltake 320 Watt, which is way under the recommended 500 watts for the 6870. Is it definitely my PSU or something else?I plan on getting a 600 watt corsair soon but I need to know if its anything else. *note* All my drivers are up to date.

GPU: 6870 1GB

CPU: Core2 Quad Q6700 @2.66GHz

Memory: 4.0 GB

OS: Windows 7 64 bit

Im playing at 1920X1080 resolution.

 

[amuffin]

Bottlenecking.

Though i don't see how you're running that system on a 320Watt.

 

[andrewcarr]

This is why I say never to use PCI-E power adapters.

How that PSU is running that computer who know. But you most likely are being limited by your CPU also.