I’ve been shopping for a replacement motherboard and CPU for my M350 case for a long time. It had an Atom board in it for a while, but it was such a poor performance/power consumption combination. The Intel DQ77KB fits fairly well, but there are two modifications you need to make. First, the power switch and LED wires are too short to make it to where the headers are located on the mother board. You need to either get new header wires or bust out the soldering iron and make the longer. Second, if you want to use a 2.5″ drive (and not an mSATA drive in the PCIe slot), you need to make some new holes in the hard drive bracket. The stock HSF unit that comes with a standard i3 CPU crowds is slightly too big and there aren’t many options for smaller coolers. The picture below shows where you need to drill. I only have two screws holding the HD on, but it’s very secure. I used some little rubber spacers to prevent the HD from coming into contact directly with the bracket.
This combination of motherboard, cpu, single 8GB dimm, and a 7mm single platter 250GB drive uses 21 watts when idle. I should mention that I’m using an old 90W Dell laptop power supply for this board.