play a DVD , see if the frame rate is affected watching a film offline.
http://www.bit-tech.net/hardware/graphics/2012/10/04/evga-geforce-gtx-650-1gb-review/1
Specifications
Graphics processor: Nvidia GeForce GTX 650 1GB, 1,058MHz
Pipeline: 384 stream processors, 32 Texture Units, 16 ROPs
Memory: 1GB GDDR5, 5GHz effective
Bandwidth: 80GB/sec, 128-bit interface <<<<<<<<<<<<<<<< Your Video Bottle neck.
Compatibility: DirectX 11.1, OpenGL 4.1
Outputs/Inputs: DVI x 2, HDMI
Power connections: 6-pin
Size: 152mm, dual-slot
Warranty: Three years
256 or 384 bit memory interface is better. read the link this is a Budget card. Buffer the full movie
do not run to many browser tools. i un installed my chrome and silver light , Turn off plugins when you stream movies.
my browser became faster. i use fire fox. watch in a smaller window.
personally i would up grade your PSU to 800watts. does not mean you have to.
i use a 1000 watts. just to be safe.
when i first read this post , i though its your internet connection. you rig looks fine.
i had browser issues last week with virgin media , low and behold it was an SNR signal problem