I haven't found a USB stick yet that runs at the same speed as the internal drive. I've got three USB3 flash drives here, one of which is especially fast, but something about them just runs slower than a HDD when booted. Not sure why that is. I suspect it has something to do with individual file IO being slower while single large file copies do much better.
If you want to boot off another OS, the best option is to partition your hard drive and install both onto separate partitions. That works fine if you have the HDD space to spare. Otherwise, use an external hard drive. An external thunderbolt-connected SSD would be ideal. (I have a lacie rugged thunderbolt/usb3 SSD that works better than anything else I've ever had)
Last edited by alternaut; 06/10/15 01:12 PM. Reason: Changed title; see note in post 34609