You've two choices, really.
i3-4350 or similar, that's dual core 3.6GHz with HT. Stick it on a B85 board, and you'll end up with something that idles around the 22-24W mark. You'll need to add a HBA for 10 drives.
AMD FX8320E, 8 core 3.2GHz turboed to 4GHz. Stick that on a decent 760G board (I like the Asus M5A78L-M/USB3). You can have ECC if you want then. Idles around the 45W mark. Again, you'll need a HBA.
The AMD uses more power, but it's fast. Also a little cheaper, the board is about £33, the chip is around £100. That's board and CPU for the price of the Intel chip alone.