While the Lexar Professional 1000X (150MB/sec.) cards will work in the D300, the Maximum write speed of the D300 will be the limiting factor. There is no sense in paying a premium for speed that the D300 can't take advantage of. I use Sandisk Extreme Ducati and Extreme IV 45MB/sec Cards in my D300. I have not tested the speed of my Sandisk 60MB/sec. Cards which might Clear the buffer slightly faster, but I suspect the difference will be very small. Good Luck and Enjoy your Nikons!