I bought a Lexar 16GB 800x CF card for my D800 a few weeks ago. I also have Sandisk 60MB/sec and 90MB/sec CF cards. I have a Sandisk 90MB/sec SD card in the other slot but it is only for overflow. When I am at the speedway, I like to set the shutter at CL so I can capture the start, finish and "racing incidents" on the track. So for me, fast cards are good for fast cars. I did a little experiment with my cards. With the shutter on CL, I fired off 10 shots and measured the time from the first shot to the green light off. The Lexar 800x took the longest. The Sandisk 60MB/sec was about 5 seconds faster and the Sandisk 90MB/sec was about 15 seconds faster. My test methodology may be disputed by some here, but I think the Sandisk 90MB/sec will be my speedway card. As noted in an earlier reply to this post, the Lexar 800x has a slower write speed than read speed. Sandisk read and max write speeds are the same.
I'm sure people shots and such, the Lexar 800x will work fine for me. It will probably be working Christmas day.