I'd probably leave the 2D profile set to your default speeds. As long as ATITool is in the tray and your 3D profile is set to your overclocked speeds, whenever you run a 3D application, ATITool automatically overclocks your card. Running your card overclocked in 2D mode puts unnecessary stress on your video card. Basically, you get the performance only when it's needed. This is one of the many reasons why ATITool is the best ATI card overclocking tool out there, IMHO.