Memory cards - SX10

--I've read a few threads and some of my camera manual, but still have no idea of the read/write memory speeds of the camera vs. a suitable memory card for the SX10, in the sense that there's no need to buy a class of card way higher than the buffer-emptying performance of the camera. Plus I don't understand card claims of high speed coupled with a lower speed (4 or 6 rating) advertised for the product - is it just that no one has instituted a 12, 15, 20 speed rating yet?

I would like to have a card > 4Gb so I can do video recording without a card restriction, but at a class rating (and price) that matches the underlying performance of the camera. Since prices for cards in Canada don't seem to fallen as low as in the US and are still a generous proportion of the camera cost, I am looking for a recommendation for a minimum memory card which will suit.
Thoughts?