My wife has just bought a 600D (T3i) and we are wondering what speed SDHC card it needs for maxiumum performance shooting stills (3.7Mb/sec at 18 megapixel RAW). She has a Sandisk Extreme HD video card (30Mb/sec) apparently it is a Class 6 card. The 30mb/sec would suggest to me a speed of about 1.8 frames/sec (30MB divided by 18MB) - or do the maths work differently to that? I have had a look on the net for information about SD cards for the similarly-specced 550D but can't find anything. Any help appreciated!