Update - 1D X results:
95 145MB/s (according to the package) write: 51 frames
-Sandisk 90MB/s write: 52 frames
-Sandisk 150MB/s write: 57 frames
This is interesting and shows that the buffer size or the interface in the 1DX is different than the 5DIII, but all of the results are excellent given that the Sandisk 1067x card is delivering a burst depth of 35 RAW frames in the 5DIII (vs. the rated 18) and 57 RAW frames in the 1D X (vs. the rated 38). RAW+JPEG to the two Sandisk cards topped out at 15 frames, FYI.
Bottom line - the fastest Sandisk cards rock the 5DIII, while the older Sandisk cards are a great deal for the 1D X. Lexar doesn't quite ive up to their specs, at least in these two Canons.
Also, on a personal note, the 1D X may only be 2x faster on paper, but the thing sounds about 20x faster than the 5DIII. I can't wait to shoot with it...