Just a quick update on my build and experiences with the components I ended up going with:
Intel G620 cpu
Intel DH67GD motherboard
2 sticks of 2gb Kingston RAM
Fractal Design Define R3 case
Seasonic S12II-330Bronze 330 watts 80plus power supply
5 Hitachi 5K3000 2TB drives(5900rpm low power drives)
As I was aiming for low power draw, I had a powermeter measuring consumption with different OSes, options, and found out something interesting.
Win 7 Ultimate:
- Booted off an external eSATA drive. Without the 5 HDs powered up, at idle, the rig drew 23W. This was just to give a baseline for system power consumption of just the CPU,motherboard without drives hooked up.
- With 5 drives powered up, and idle, it drew about 46W
- With 5 drives powered, but spundown(ie. after hard drive inactivity for x mins), drew about 29W.
FreeNAS 7(freeBSD OS)
- Booted off a usb disk. Running the lastest distribution, the system had problems recognising the Intel Gigabit Ethernet built-in to the motherboard(82579V controller). After I managed to find a test distro with the latest intel drivers compiled into the kernel, I then ran into another problem as I found that the drives hooked up to the SATA6 ports wouldn't be recognised. Again, put it down to old drivers not supporting chipset. Gave up on FreeNAS7, even thought that was my first choice for features,etc. What I did find was that power consumption of the rig at idle running Freenas7 without the hard drives hooked up, it was about 31W, even with the power saving management features turned on. Played around with it a bit more, but couldn't get it down. Seems the power saving management of freeBSD(powerd) consists mainly of throttling the cpu. Even after my cpu was throttled to 350Mhz, there was negligible power savings. Seems that the sandy bridge cpus seem to not need to throttle down the cpu speed to save power....but I concluded that maybe freeBSD was missing perhaps the same power management features as other OSes, as I could never get it down below 31W.
FreeNAS 8(freeBSD OS)
- Booted off a usb disk. Drew about 31W at idle without drives hooked up(same experience as with FreeNas7, couldn't get it down further)
- drivers in latest freenas 8 seems to work with my config, ethernet controller was recognsed properly, and so were all the drives.
- With 5 drives powered up, and idle, it drew about 53W
- With 5 drives powered, but spundown(ie. after hard drive inactivity for x mins), drew about 37W.
Ubuntu 10.04(Linux OS)
- Booted off a usb disk. Drew about 25W at idle without drives.
- With 5 drives powered up, and idle, it drew about 48W
- With 5 drives powered, but spundown(ie. after hard drive inactivity for x mins), drew about 30W.
Conclusion I drew from all that testing was that, surprise surprise, Windows 7 was the most power efficient OS... That was really surprising to me as I expected Windows 7 to be comparatively bloated compared to the FreeBSD and Linux distros. Ubuntu wasn't far behind it in terms of power efficiency, just 1 watt or so diff. The freeBSD distros however....drew a fair bit more power than both Win7 and Ubuntu.
However, as I wanted to run this box as a NAS and boot of a USB disk, I had to write off Win7 as the OS of choice, and went with Ubuntu Server, as that allows me to boot the OS off a usb flash drive, and is quite power efficient as well, idling under 50W with 5 drives, and once drives are spundown, about 30W, which I think is quite good.
Also, with the case I got and power supply, with just the stock fans(1 intake, 1 exhaust), I can't hear the machine, and the temps all look fine(CPU at about 28 degrees and HDs about 30-33 degrees). Under load, temps go up a bit, but not much noticeably and machine is still quiet
are already out . 
I thought it was a newer version of the g620 . 