I may as well give up on looking for a new mATX mobo w/SATA III ...especially since I probably won't find one as good as my ATX M4A89GTD PRO/USB3 it would be a downgrade. I figure these are my options:
1) Probably lowest cost is to use my existing Sonata One ATX case and mod it if necessary, the ASUS 890GX board should squeeze in there but only has USB2.0 in front (not a deal-breaker). It is 8 inches wide so it will definitely fit the x6 hs/f, it may fit my better air coolers, or I may have to get a watercooling solution that will fit where the 120mm case fan is in back. I see a few for sale on the egg for <
$100. Downside is it only has passive intake in the front, and little holes that spell out "Antec" on the sides so a case mod may be necessary, don't know yet. Perhaps watercooling with radiator/push fan on the inside and a pull fan on the outside could cool radiator AND inside case at the same time? My hard drives heat up when the side panel is off due to no front fan so they would benefit from a 80mm front side panel mod. Currently my 555BE unlocked to 4 cores only gets up to 50C max in this case, but who knows what the x6 will do maxed. I don't plan on OCing it, but may have heat issues if I do need to max out all cores while videditing for extended periods.
2) ATX mid-tower cases that are 18.5" or less deep, I've seen some cheapies and some more expensive. Most I've seen have better airflow than my Sonata. Most of those though come at a further price--width is usually around 7 1/2 inches so I would most likely have to use the stock x6 heatsink fan or purchase a watercooler with a single 120mm radiator/fan.
Here is what my back panel looks like, it appears that a Corsair H80i or Ttake or Antec Kuhler 920 MAY fit where the 120mm case fan goes now.
I have been jones-ing for one of those light watercooling setups anyway (leaning towards the Antec Kuhler 920 since Bubba likes those), maybe that should be my first priority and then see what it will work with as the second step?