I am a fan of 'middle sized' storage. Too little and you get frustrated, too much and you run the risk of bigger data loss. I have a mixture of Class 10 and UHS Class 3 and have a mixture of sizes. I generally use a 32GB UHS card in slot 1 to write RAW images and a 16GB Class 10 in slot 2 for JPG. I have not noticed any issues with doing this. For the rare times I shoot video on my DSLR I always go for the UHS cards.