I've recently used SanDisk "Ultra II" cards in 2 GB, 4 GB and 8 GB capacity. All have passed the MT II's built-in media testing with "96/24" results.
I had one lockup with the 4 GB card in some 50 hours of recording this past week, but the S/P-DIF stream from the (AC-powered) preamp/converter was being repeatedly interrupted by power brownouts at the time--so I don't particularly believe that this lockup was attributable to the card itself. Besides, I was using the 1.0.3 firmware and the notes for the latest version (1.0.4) claim to have fixed the lockup problem, or at least a lockup problem.
However, the experience convinced me to use the smallest-capacity card that is large enough for the recording I can reasonably expect to do at one time. In case there is another lockup, recovering the data from a smaller-capacity card would surely be a much more easily manageable task.
--best regards