I own the 40D & use the Sandisk Extreme III 2GB CF card that has 30 bytes of read/write speed. Was told that a 4GB card is wasting if you're only a frequent shooter. The advice came from Pro that i have made friends with just recently.
I can't imagine any ancient Type II card that one would want to use in a 50D. Most of them were microdrives. 50D files are rather large (20MB) and the camera has a high throughput, so an 8GB card is a good match.