Low performance on my 7870
I recently built a new system for Christmas; CPU: i5-3470 GPU: XFX 7870 core edition RAM: 8gb supposedly 2133mhz, but I can only have 1833mhz, I've always felt this graphics card had low performance since I've got it, I'm getting below 15 fps maxed out at 1080p on games such as hitmam absolution, the witcher 2, and Far Cry 3. My friend had recently got a pre-built computer, of which he has the same CPU, 4gb of RAM, and a 7770, yet in games like Minecraft, with the shaders, he gets 10 more fps, but I should be getting much more than he is. Is there anything that could be limiting my card? maybe through installation problems? I should probably add, I did get a little, and I mean a really little amount of thermal paste on the CPU, but it works fine so I assumed there was no fault. please ask of any details that may be important.