first, 1920x1080 needs 82mb/s according to the ML, it says at the bottom of mine the general mb/s and it changes depending on the resolution. I just tried and the mb/s creeped up to about 91/s when I stopped it after 30seconds or so.
You may want to try the memory hack, and change the preview to hacked, as well as turning off global draw to squeeze out a bit more performance, but it may not do all that much. one of those settings may disable the liveview when you record, cant remember which(or maybe it was another).
try recording to a lower res and make sure you can do it, i think that cards speed should handle 1280x720, just to see if raw video gets recorded at all.
also theres a benchmark in the debug. theres a bunch of posts over at the ML forums on memory card speeds and the results, you will have to search for it. I can personally vouch for the toshiba exceria 1066 32gb card, does 1920x1080 easily.
I'll try those things when I get home. Thanks for the suggestions!
Are you running ML and recording on same card?
Try to run ML from SD card.
Nope, ML is running from an SD already.