Gaming with ATI open-source drivers-Collection of common programming errors

1. Consider switching to LXDE or KDE desktop environment

I think you should seriously consider switching to Lubuntu. Compiz is bollocks and it will remain so at least to late 2013. That’s if you believe it will -ever- do less harm than good, that is. Please note that you can install LXDE on regular Unity Ubuntu and choose your desktop environment at login! (session)
LXDE also affects gaming performance?

If I install any dekstop environment (like XFCE) alongside Unity can it affect Unity?

2. Re-consider your choice to use open-source ATI drivers

They are usually 3 times (yup, 300%) slower than the proprietary ones. See:

How to review the current state of open source vs. closed source graphics drivers?

If you have ATI/Intel hybrid (switchable) graphics: You can use your Intel for desktop and ATI for gaming. Switching on Linux is cumbersome for older generation hybrids though
How to re-configure graphics from Intel integrated to Intel / ATI switchable?

As for the bug you experience:
Intel vs AMD desktop performance – worse on AMD
Catalyst Tear Free option requires over 256 MB video RAM