PanMan's got it. The standard SD card has the read write speed of about a 1X CD rom disk. The Ultra is about 66X and the Extreme III is 133X. This adds up when your waiting for a screen capture, especially if your using a standard disk. One thing more on the Extreme III, its suppose to be designed for more extreme conditions.

Sandisk Extreme III 2gb SD card

The temp conditions sound familiar.

How big a card is going to depend on what you want to do. My Humminbird 997 screen captures are just over 1.2 mb each so you can store a lot of screen captures per gigabyte. Now the guys have the software working to play back recordings you may want to go with at least the 2gb to have enough room to record for a while. I haven't tried recording but the gut feeling says it uses a lot of memory per minute.

WarrenMN