may try it when I have mine, but probably be another week or two.
I think I misunderstood. I thought you meant for distribution. It would be pretty slow if you used a SDXC card as your boot drive.
According to the SD card people, SDXC has speed of 104MB/s (with a big B) http://www.sdcard.org/developers/tech/sdxc, and reaching up to 300MB/s. My brand new MBP had a maximum disk speed of 34 MB/s according to xbench.
It sounds like running OS X from the SDXC card could be up to three time faster than from the internal HD?
I'd be very surprised if that speed was found on anything but super expensive cards, or as a theoretical speed. Can't hurt to try though.. but prepare for disapointment.