About 6 Mb. No I'm being flippant! Its the processing speed I understand. 10Mb/sec v 4 Mb sec. 10 is best but I've saved a trifle buying 4 and I've never noticed the difference myself.
answered on 21 Nov 2013
It's all to do with the speed at which date can be written to the card. Class 10 will, in theory, be faster than class 4. If you have a device such as an HD video camcorder with a high recording bit rate then you would choose a class 10 card. A digital audio recorder would be fine with a class 4.
sorry can't help. bought as an xmas gift so not tried yet and took the card the camera recommended. sorry