Let’s say I have an x230 that supports one mSATA drive and a 2.5" SATA drive. Would there be any performance benefit in putting dom0 on the mSATA drive and all AppVMs on a SSD 2.5" drive (over putting everything on a SSD 2.5" drive)? Or vice versa because mSATA in the x230 is limited to SATA II speeds?
Depending on your hardware you might not even notice the difference.
I would put the most used and intensive qubes on to the fastest drive,
whichever that is.