I will be using an SSD. I had a 2.5" HDD and it couldn't cope with some P2P stuff. Even a 3.5" HDD chokes once I start hitting about 8-9MB/sec down, due to the shear number of random writes. I'll look at the Crucial one, but their reputation for quality isn't brilliant...
Curical on 3x M4 has been perfect, it just had the 5200 hours bug that i needed to flash the firmware, and they all been running solid till today. Now M500 and M550 seem to be fine aswell, just they kinda run on the hotside, this is the only reason i move toward samsung as i dont have anything bad to say about them, i dont own a MX100, just bought one though for my brothers laptop, but i heard good comments about the temperature so the reason i suggested him to go with it. But depending on your workloads you could check the Samsung 850pro or Intel 730, if you are going into heavier writing maybe would be best to check server grade ssds.
I have an old Atom based one and was generally happy with it, apart it not having many SATA ports and no real expansion options. It's not so much the size I'm bothered about, but those boards are designed for low power operation so I thought they would be best.
Atoms i have mixed feeling, i had an Acer 340 that had an atom 270 if i remember correctly, and with 4 hdds it idle at 45watts no spin down, but even with 1hdd it was very close 25W, while the i3 + intel mobo + picoPSU + 2.5 hgst idles close 10W. The atom was unresponsive at times, even transferring heavy on the networks push it over.... if i was downloading with the server, and moving a file in the network and someone else was trying to watch a movie, the movie would stutter (even if it was not in the drive was moving or downloading) was simply to much for the atom to handle.
But atom now a days are more capable, and probably more efficient, but with how good celeron/pentiums are in terms of consumption, price and performance, that the atoms don't have a place for me. That said, if you are in a budget a baytrail will be cheaper, but you will be binded to how the motherboard comes.
Personally i do want to give atoms another chance, im specially intrigued by the Intel Avoton C2750 Octa-Core, but at the current price, ASRock C2750D4I Mini ITX Server Motherboard FCBGA1283 DDR3 1600/1333
, you can even go with xeons and end up with similar spending, but still it intrigues me.
So you don't rate their mITX boards?
I own an mini ITX intel sandy bridge motherboard thats been perfect, but intel is getting out of the retail motherboard buisness, leaving it for the 3rd party manufactures, but they still did some motherboards on haswell (i kinda think this is their last motherboards), one of them is the one i linked above, there is a second that i cant seem to find.
You should check Vicotnik builds, he has very good combos, and runs a lot of picopsu setups, and he is using AsRock mobos that i also have read have had very good consumption from ivy bridge and haswell, if i can find you some examples ill post them later on.
Now on your AES need, i think i3 and higher support it, so maybe something like Intel Core i3-4130 Haswell Dual-Core 3.4GHz LGA 1150 54W Desktop Processor Intel HD Graphics 4400 BX80646I34130
+ ASRock Z87E-ITX LGA 1150 Intel Z87 HDMI SATA 6Gb/s USB 3.0 Mini ITX Intel I217V Lan 802.11ac WiFi Intel Motherboard
(to furfill your 6 sata desire) or ASRock B85M-ITX LGA 1150 Intel B85 HDMI SATA 6Gb/s USB 3.0 Mini ITX Intel Motherboard
(if you were to be fine with 4 sata ports).