Dave, I'm shooting with the same Lexar 1000X as you are in the slot. I know the focus system is brilliant in comparison, so i'm hoping that makes up for the lost fps..
Essentially I'm trying to justify to myself that I 'need' the 1dx
when really, for what I shoot a mk3 would be adequate!
Do you use the in camera HDR or photo stacking in your 5d3?