I did a 554MB backup using save-nand onto a 2GB factory-formatted USB memory stick in about 10 minutes. That was with Q2E17 firmware that came with build 8.2-760. My XO is a lot easier to backup than my Windows PC.
With Q2E18 firmware (from build 8.2-763) a 480MB backup using save-nand took just under 4 minutes, using the same 2GB memory stick as above. Restoring the image using copy-nand took just over 4 minutes.