Not MCH (hur hur) as I don't actually know what they are for, and their limits, and the internet hasn't helped greatly![]()
The MCH is basically the Northbridge, the VTT is also known as the FSB termination voltage but I can't quite remember what it does exactly but upping both voltages with help with stability. I needed to tweak both of mine to get stable at 3.8GHz from 3.55GHz. Try 1.3v for both if they're lower than that, 1.5v should be fine for the MCH and 1.4v for the VTT.