For 1080p video, a CF card with about 10 MB/s sustained write speed should be sufficient. In CF “x” ratings, that’s roughly 66x, which is similar in idea to an SD Class 10 card.

For continuous RAW+JPEG shooting, faster cards help the camera clear its buffer sooner, so you can sustain longer bursts and recover faster between bursts. A slower card will still work, but it can reduce burst depth and write times.

Community reports suggest the 7D can benefit from very fast cards, and may even be limited more by its own internals than by top-end CF cards. So while the minimum for video is around 10 MB/s, a faster card is the better choice if you care about continuous shooting performance.

Practical takeaway:

• Video only: about 10 MB/s minimum
• RAW+JPEG bursts: buy the fastest reliable CF card you can reasonably afford

A faster card won’t increase the camera’s frame rate, but it can improve how long you can keep shooting before the buffer fills and how quickly it empties afterward.