4870 Low GPU usage when gaming

First, sorry if this is a repeat subject, I've searched here and google, and couldn't find anything that would solve my problem.

System specs:
CPU: Phenom II X4 940 @ stock
Mobo: Biostar TA790GXB
GPU: ATI Radeon HD 4870 1gig
RAM: 4gb OCZ Reaper DDR2 800
HDD: Old 7200rpm SATA seagate 200gb
PSU: OCZ modx 700watt
OS: Windows 7 RC 7100

I bought and built this rig recently and have been noticing some disappointing performance with Warhammer Online in specific. I've not tested this with many games aside from L4D and the Heroes of Newerth beta, but both games perform flawlessly on the highest settings @ 1440x900 (although they also show low GPU usage). I have the latest video drivers, but have not updated BIOS, doesn't seem likely to be the problem, but I'll try that out tonight.

As I said, Warhammer is giving me the most problems, with 30-60 fps in the world questing alone, 15-20 fps in rvr Scenario's with give or take 20-30 players on screen and a literally unplayable 2-6 fps when assaulting keeps (60+ players on screen) with in-game settings maxed (except shadows, Balanced) and forced AA 4x/AF 2x in the catalyst control center. I would accept this poor performance if the GPU was at full load, but as it seems now, it's not really being used to it's full potential. I've toyed with pretty much every setting and have noticed recently that the GPU does not go above 30% load at any time no matter how much action is being thrown at me in game. GPU-z and Riva Tuner show an average of 20% usage at all times while playing.

A friend built a more expensive system around the same time (core i7 / 6gb ocz 1600 / Radeon 4870 1gig / 15k SAS HDD ) and although his rig destroys mine, we both bought the same video card, but his GPU load seems to operate properly up to the high 90%'s in highly populated RVR situations with only slight loss in FPS averaging 30-40 no matter what.
Looking at my own CPU and RAM usage while playing, they're both at 40-55% at any given time, so I don't think that could be the issue. The GPU remains at 20-30%.

Any ideas? Any info, help, advice, links, whatever, would be very very much appreciated.

For online games your internet connection can affect your frames as a good deal of time can be spent waiting for packets and organizing those that arrive corrupted or out of order. Also, your GPU could be bottlenecked by your CPU. You can help alleviate this by overclocking your CPU. As photon boy suggested you can also take the above steps to try and eliminate possible driver problems.