Haha...you are another Photoshop CS6 LAG Victim, me too, the LAG has been torturing me for 1 year and I have spent nearly a year to finally find out the solution.
Read my thread to help you solve the LAG problem Photoshop CS6 bugs + lagging ??
The solution is, I give you a rough step-by-step guide
1. Download the White Windows Workaround plugins and then install accordingly (link is in my thread)
2. update whatever MAC OS / PC OS to the latest possible versions and update Photoshop CS6 to latest version.
3. Spend 1 full day or 2 days (at least) to adjust only the Photoshop > Preferences > Performances
Hahaha....I spent 1 year learning this