Some Time ago Rob Galbraith had tested the speed of many different cards in the D300 and published the results on his site. I went there yesterday to check for the latest info before answering your question and only the D300s was listed and there were no test results were available. When the D300 was introduced back in 2007, 30MB/sec. Cards were about the fastest available. The 45MB/sec. Cards were introduced about the same time. At the time, the Sandisk Exteme Ducati CF cards performed the best in the D300. If I remember correctly 8GB cards were the largest capacity available. Good Luck and Enjoy your Nikons!