As far as SD cards go, the real experienced and knowledgeable users of this site (not me) have said multiple times over the last couple years that the speed of the card won't really matter for *recording*. I believe a Class 2 SD card has almost double the speed necessary to easily handle 24/48 or 24/96 recording. Key phrase being almost double... so even with a Class 2 card it's not close enough to worry about, since it's about 2x faster than the speed used for 24-bit recording. I've seen this subject come up here and there when someone asks about getting a higher class SD card, and if it's "more safe", but according to all the most well-known users here with high post counts, it's not.
The higher speed will certainly help transfer times though. Some people have also mentioned the possibility of higher-speed cards actually having potential for errors if the speed is achieved using a burst-method, but I don't believe anyone has actually confirmed that it could cause a problem with a given recorder.