We have a clear winner, but not an awardable one: the Asus P5E3 Premium (Compare Prices on P5E3 Motheboard) was the only motherboard in this comparison to pass every single test, because the remaining boards failed (or partially failed) four-DIMM compatibility. But we realize that some builders will never use more than two memory modules, and that the higher capacities available with DDR3 make large dual-channel kits a better option. Awards are reserved for obvious leadership in performance, overclocking, or "bang for the buck", and these are places where the losing motherboards each had their own strengths.
Gigabyte's X48T-DQ6 and MSI's X48 Platinum both matched the P5E3 Premium in CPU overclocking capability, taking our E6850 to 446 megahertz FSB clock at the processor's default 9x multiplier. Yet the MSI X48 Platinum's 452 MHz maximum FSB at 6x CPU multiplier edged out the Gigabyte X48T-DQ6's 540 MHz FSB, leaving the P5E3 Premium at the bottom for multiplier-limited processors at 535 MHz FSB clock. This slight win for MSI put the Gigabyte X48T-DQ6 in second place for maximum achievable FSB clock as well as four-DIMM capability.
All three motherboards provided similar performance, yet there's a large price disparity between Asus and Gigabyte/MSI models. Though none of the boards we tested had reached vendors in time for any direct price comparison, we can look at otherwise-identical X38 counterparts to see the trend: As of this writing, the P5E3 Deluxe WiFi-AP @N Edition costs $350, while the MSI X38 Platinum and Gigabyte GA-X38T-DQ6 are both $285. For builders who only want to use a single pair of memory modules, that $65 price difference could be the deciding factor.
On the other hand, anyone who has second-guessed themselves concerning the overall value of the X48 Express probably shouldn't have bothered to do so. Our X38 Express motherboards overclocked just as well, and all of them supported Intel's latest FSB-1600 - the reason for which the X48 was released. A few of our own editors would claim that the X48 Express should be the default choice for FSB-1600 desktop processors, because nothing is certain in the world of overclocking, but we've yet to present any evidence of an X38 motherboard that was not perfectly stable at speeds beyond FSB-1600.
A higher "validated" speed is no guarantee of increased clock speed potential. The idea that the X48 Express is better than the X38 Express in the same way that a Core 2 Duo E6850 is better than a Core 2 Duo E6750 can be shot down by the fact that our E6850 doesn't overclock as far as our E6750. One could point to the higher memory stability of the P5E3 Premium - when compared to the P5E3 Deluxe - as proof of the X48 Express chipset's superior stability, but minor differences between PCB revisions 1.03G and 2.00G between the two models are more likely responsible for this benefit. One might also expect that the P5E3 Premium BIOS is optimized for added high-FSB stability rather than the best performance, but the P5E3 Premium outperformed the P5E3 Deluxe. Retail buyers should expect the latest PCB and BIOS revisions to be applied to either model, and we're left with no evidence that the X48 Express is actually a better product than the X38 Express.
How much more should you expect to pay for a product that's better in theory but not practice? We expect the price premium to drop to around $20 once retail channels are completely filled, but early buyers can expect much higher over-charges for what are, electronically, the same products as the X38-Express models on which these are based.
If X38 Express motherboard prices remain consistent for X48 Express versions, buyers who only plan to use two memory modules could find better value in the second-place Gigabyte GA-X48T-DQ6. But at these prices we can't imagine too many buyers will be willing to pay even more for an X48 Express Northbridge, and manufacturers may be waiting for X38 prices to drop a bit before shipping X48 derivatives.
In the end, the difference between the X48 and X38 Express is at best 98% marketing and 2% validation. Buyers who constantly find themselves among the unlucky few should consider the X48 Express as insurance against high-FSB stability issues, but everyone else could potentially find better value in the X38 Express.