Overclocking the QX9650 was a grisly experience as Intel offers a limited selection of tools in the BIOS. We reached a speed of 3.42GHz, which is pretty feeble, but we did it in a different way to the 3.42GHz that we got from the same processor on the DX38BT.
On the X48 we got the best performance by keeping the multiplier of the Extreme Edition processor static at 9x and raised the front side bus from 333MHz to 380MHz. That allowed the memory speed to rise to 1,520MHz but once again we were unable to separate the X48 from the X38.
The Asus Rampage did a far better job with the QX9650, overclocking as it did to 3.66GHz. This delivered loads more performance despite its reliance on DDR2 memory running at 1,066MHz. Check the Rampage review and you'll see that we weren't especially impressed with its behaviour yet it still managed to dance all over the Intel boards. We reckoned that the Rampage would benefit from a BIOS update which is a safe bet for any reviewer and is the equivalent of your doctor telling you to stop smoking and to take more exercise. Nonetheless Asus has issued BIOS 0401 for the Rampage, which is claimed to help memory compatibility, so the performance may have improved since we reviewed this model. However, we didn't have the Rampage to hand so were relying on our original test figures on BIOS 0219.
Switching over to the Core 2 Extreme QX9770 we could no longer use the DX38BT for comparison, as it doesn't support this processor, so it was a straight fight between the Rampage and the DX48BT2.
We were surprised and annoyed to find that the DX48BT2 wouldn't allow us to run the memory at 1,600MHz even though the setting is present and correct in the BIOS. We overclocked the QX9770 from 3.20GHz to 3.78GHz with a combination of an increased clock multiplier and a 20MHz addition to the front side bus which raised the performance by a healthy 11 percent. Overclocking the Rampage was much easier as we simply raised the clock multiplier from 9x to 11x to get a slightly higher speed of 3.80GHz. The extra 20MHz is neither here nor there but the increase in performance was 14 percent. When we tried the same settings on the DX48BT2 it refused to POST.
We can learn a few lessons from this comparison. For one thing the DX48BT2 doesn't live up to its billing on memory support as it won't hit 1,600MHz. More disturbingly you can get better memory performance from the Asus Rampage using slower DDR2 and that's especially true if you overclock the processor.
The Rampage delivers better performance at stock speeds, overclocks better and in every measureable way it is a better motherboard than the DX48BT2. That may sound like a harsh judgement as the Intel board does a reasonable job but it is short on features and performance yet it is priced at the same level as the competition when it actually needs to be a fair amount cheaper.
We were disappointed that the DX48BT2 didn't make full use of our 1,600MHz memory but it's the low performance that would make us nervous about recommending this motherboard.