The latest generation SD cards have significantly increased in speed, but still lag far behind Compact Flash cards. Top rate CF is capable of write speeds of 90 + Mb/s BUT the D300s is only capable of writing about 30 - 32 Mb/s so there is no real advantage in paying for a much faster card, except that when transfering via a card reader to your computer, the faster read speed is an advantage. Regarding size, I stick to max 8Gb cards. This gives me bout 400 images per and reduces the loss if one goes "bad" (I have had 2 Transcend CF cards do that over the years and am stopping using that brand for that reason). Additionally I am set up to write all to both cards so I have an immediate backup, it does slow things down a bit, but I feel safer doing it like that. Each to his own though!