Try upping your MCH a little.
It will possibly allow you to get more out of it FSB wise.
|(G)MCH OverVoltage Control: This is the Northbridge voltage. Most overclockers will not need to change this setting. Change this to increase stability under certain FSBs (i.e. 420Mhz+). Note that an increase in this setting WILL produce increase motherboard heat output. A Northbridge cooler is recommended for most P35/X38 motherboards even if you are not changing the MCH voltage. Gigabyte motherboards with out Ultra Cool should have a small Northbridge fan ( I noticed a 8C drop in my motherboard temperatures once I installed a 40mm fan on the heat sink on my P35-DS3L.).|