In the process of specing low power hardware for benchmarking. Data center space is at a premium here in Manhattan and we're up against power limitations. I/O is the bottleneck, not compute. CPUs currently maxing at <25%. Still have plenty of rack space, though! ;-)
Dream hardware would include: low power CPU; efficient MB/Chipset combo with support for single CPU, ECC RAM (buffered or un-buffered) and PCIe X16 mechanical/electrical interface.
Intel makes this easy with their C204/LGA 1155 with support for Xeon E3-1200 / Core i3-2100 / Core G8X0 / Core G6X0.
AMD on the other hand, appears to make it difficult to use the same platform with their Opteron 4200s as well as consumer CPUs. The other option for AMD's products is two separate systems; one for C32, one for AM3+. But I can't find any AM3+ boards with full support for ECC RAM.
We want to benchmark the hell out of all hardware options/distros/DBs/etc before we commit long-term to a platform that must quickly scale over the next couple of years. Would love to include ATOM in this process. But support for ECC RAM seems to be non-existent there too. Targeting 100w system TDP (125w "at the wall").
We're including separate workstation benchmarks as well, hence the PCIe X16 requirement.
I have heard a report recently that AMD will be re-introducing Opteron processors with compatibility for their desktop socket platform.
It used to be that AMD had AM2 compatible Opterons (I actually have an old test system still running one of these) that you could use in a regular AM2 board with or without ECC memory. This was perfect for someone looking to use server-class parts for a simpler system without the greater costs of some of the higher end server-class parts.
If you are looking for low power draw and ECC memory is a must, with the hardware generations currently available, then perhaps your best bet will be to use the LGA 1155 Xeon processors. Very powerful processors and the versions without integrated graphics cores are 80W. I've seen several kits of DDR3 1333 ECC running at 1.35V, and a good workstation graphics card, such as the Quadro 600 would be ideal workstation performance without requiring much additional power draw.