Ace, check this thread for some hints and info

To boot at high FSBs ( higher than 450MHz ) you'll need to relax your timings, and then re-set them to what you want through MemSet within Windows.

The memory dividers ( FSB/DRAM Ratios ) play a big role in overclocking in every X38/X48 motherboard, and the GA-X48T-DQ6 is no exception.
You need to choose the best divider for the desired FSB.
Also note, that the FSB Strap control is "integrated" with the DRAM/FSB Ratios.

Also make sure you're running BIOS version F4H ( I've posted a download link for it ).