Bit-Tech published a review of Gigabyte's X38-DS5 and X38T-DQ6 motherboards

Simply ignore DDR3-based X38 boards for the time being because there is literally no extra performance on offer - this is very likely not unique to Gigabyte though. Even then, as a top of the range DQ6 board, I don't feel the box package and the overclocking capabilities are where they should be. There's nothing over and above the DS5 apart from different capacitors, a few more power phases and a Gigabit Ethernet socket. The GA-X38T-DQ6 is a good, stable board at stock speeds but I'd still buy the GA-X38-DS5 which does the same for less, without the extra burden that is the cost of DDR3 memory at the moment.

If you feel the overwhelming desire to buy an X38 board over P35, then the Gigabyte GA-X38-DS5 should certainly be one to consider even if you're not that cost concious. It performs very well, has plenty of features, is super stable and has the same BIOS options as the DQ6. However, it's not a great overclocker like an X38 should be and offers virtually no performance advantage over cheaper P35-based boards.

Gigabyte X38-DS5 & X38T-DQ6 Review