@athimbleofdan your number still seem low. As I recall it is not valid to benchmark the card in playback mode, the results are always higher than you get with other modes. I believe that the live view needs to be enabled during benchmarking to get an accurate reading of how the card will perform when recording raw.
With your 1000x card you should be getting around 75 MB/s when recording raw, the 56.4 MB/s you are getting is similar to what I see with my 800x card. I believe at this point continuous shooting at 1880 with 16/9 ratio is not possible with any card, the MK5D2 body doesn't quite have the speed required. As of now, if I remember correctly, I the highest resolution I can get continuous shooting is at 1880 with a aspect ratio of 2 (1880x940).
Things have been changing quickly so I may be wrong on some of the specifics however.