> Is there a drawback to using 2 different drives for samples?
The more distributed the sample library, the better - especially when you carefully plan storing different type of often used samples over multiple drives.
A regular SSD, even lower end ones will out perform about 5 times better than a 7200 rpm HDD (as least for reading data).
* Based on estimated round up of 99% usage (HDD) compared to 19% usage (SSD) in this test :
http://forum.cakewalk.com/FindPost/3503896 You will even get double SSD performance by doing a RAID-0 setup (no safety, but I guess it's ok for read only samples that you already have a backup plan).
* Based on the above test link, comparing 10% usage (RAID-0 2x SSD) compared to 99% HDD.
I've no experience in PCIe SSD vs SSD, but unless your need is 5x higher (edit : in performance) than your current HDD, I guess one or more SSD will be sufficient, regular or RAID-0 setup.