Terrible performance/lag regardless of build/settings..?

I'm at a complete loss what is going on..

I've a reasonable rig: i7 920 (DO) @4.0GHz, GTX 670 Windforce 3x, 8Gb DDR3, @1920x1200 but everything I've tried (Gamecube & Wii) is lagging & stuttering terribly, screen tear is also dreadful even with the option enabled,
I've tried different builds & pretty much every combination of settings from the lowest to the highest.. and am seeing no improvement, I appreciate it's most probably something I'm doing wrong but I've absolutely no idea what.

Any help would be greatly appreciated.

Thanks.