Hi,
I am just wondering, is there any real advantage to getting a Class 10 SDHC card? Only I usually just take photos (very rarely 720p HD video) on my SDHC Class 4 card. Not sure if a class 10 helps when viewing photos on the LCD screen etc?
No.
Where a fast card will help is if you need either:
(a) shots offloaded from the camera's buffer to the card quickly,
(b) photos loaded off the card into the computer quickly.
Video doesn't touch on any fast card's abilities - even at something like 25Mbits/sec, a fairly generous rate for H.264, that's still only 3MB/s. The class rating for SDHC is a minimum sustained write speed of that many MB/s - ie, for 1080p video, you'd technically only require a Class 4 card, if that.
Rather, if you're in the situation where your camera's buffer's just filled up with a few rapid shots of some wildlife or sports sequence you've taken, the more quickly it can dump that to the card and let you resume shooting, the better. Even with a good 20MB/s card - no great feat in 2012 - that's still half a second per D90 sized RAW. Drop down to a relatively slow card, and you could be easily kicking yourself for losing a good shot.
As for getting them off the card, you're then likely to be limited by the speed of the reader - even ExpressCard/34 readers often only use USB 2.0; faster ones tend to be significantly more expensive.
In summary: don't worry much about card speed, unless you're into wildlife or sports photography. But, with prices as they are, there's little gain in going with slower cards anyway.
