We will look at WRITE speed as this is the main factor affecting saving the image you take. So if you buy a standard card from SanDisk for example, the interface speed will only be 30 or 33x WRITE.
Hence I've settled for the 60X WRITE and 66X READ SAN DISK ULTRA as I don't mind paying the premium if it improves the quality of the image (learned from SanDisk engineer although he told me that the standard card is good enough).
The benefits of using a faster interface card is that it optimises the saving of videos (not so much on shooting bro ortega)... With a faster interace. ALso according to San Disk guy (I stress.. he recommended NORMAL speed) that the speed would also affect the image quality (Slightly) but not significantly. So to each on its own... For me, I go for faster speed as it gives me option to use my card for other cameras.
Canon engineer adviced me to buy SanDisk as they've experienced sporadic problems with other manufactuers (so far no problem from SanDisk and Toshiba).CHEERS!!!