Been looking at cameras for a couple weeks now, planning to upgrade in the next few months hopefully. Wanting to go from an XSi to either a 7D or 5D MkII. Noticed these use Compact Flash cards instead of SD. I have several SD cards and have never had one to go bad. Why are these higher end cameras using these big bulky CF cards? From what Ive seen, they cost way more per GB than an SD of the same size.