Likely yes. When the D300s came out and started doing video the fastest CF cards were 333x and 500x (roughly 20-50MB/s).
I am a geek and not typical, but usually try to get the fastest card i can when buying. Reason being more for transfer speeds when importing photos on my PC, plus quicker writes from the buffer when shooting shots quickly. Not sure on video since i have the D300/D700 w/o video ability.
I have some 32GB Lexar 1000x cards that ROCK! Sooo fast. I've individually baselined each at over 90MB/s (rated in a perfect world for 100-120MB/s iirc).
like i said earlier though, the bottleneck is going to be the camera not the card. When the camera can only write 20MB/s and even if the card *can* go faster - it likely won't help. However then transferring pics to your computer will be faster!