Are the Lexar Cards really that magic or am I doing something wrong? I got a little excited and tried to test things out again but can't get anywhere near those speeds, i have to step down to 1728x972 to shoot continuous 16:9 on a Transcend 32gb 1000x. Or instead I shoot 1880x800 anamorphic and upscale to 1920x816 for 2.35. Last summer I assumed Transcend had really good build quality, but does the brand of the card make that much of a difference?
Tried on both Oct24th Build and the Newest Build
Yes I thinks so, Lexar 1000x cards seem to work better with 5d2, but my 64GB card is faster then my 32GB.
I always get better number then most, I usually shoot at 2:1 or 1.85:1 (1873x936 mlv & 1880x1014 raw)
Crop mode for continuous at 2048x930 (that's my favorite size)
*Note* even thou I can record at 16x9 (large frames 1880,1872) its not stable with HDMI devices, I choose to use 1.85:1 or 2:1
with those sizes .

Edit: Also check your card for being fragmented , I notice when the card slow down a little it's always fragmented by about 30%.
If you are working in Windows , I do a disk defragment & the speed always return . FYI the maximum write speed I have seen on
my 5d2 with Lexar 1000x is 79.8 MB/s ,but only in Crop mode 1:1 is around 75 MB/s on average.
For MLV try the Nightly Build from Feb16th, that seems to be the Fastest I have found to work with 5d2 @ 1872x936 2:1 .
That's the one I use for paid work, after that date things started to slow down and became unstable.