Thanks for your response. I did follow the instructions here:(http://arduino.cc/forum/index.php/topic,108542) which I believe modifies the oled libraries to use hardware SPI. It was certainly faster at drawing the example graphics after the modifications.
WRT to the SD card CS pin, this site:Data-Logger Shield for Arduino shows the SD card using Pin10. So I think I've done it right, but I might be wrong.
Thanks again for you help.