ATI Graphics, should I use the proprietary driver and how do I do it?

There are far too many different sets of instructions and such for me to feel confident. Though the OSS driver works shockingly well, if I can get even better performance I would like to. I use Second Life sometimes, and this is why I’d like better performance. ATI hardware is totally new to me.

00:01.0 PCI bridge: ATI Technologies Inc RS690 PCI to PCI Bridge (Internal gfx)