Mixing Drives and Interfaces on an Intel Raid Controller
 

So mixing and matching is doable on modern non proprietary controllers and though this is an Intel controller I have done much the same on AMD controllers. The manuals even say you can do it but yes it is recommended to use the same size and interface but that is recommended it does not mean it is a rule. Yes it is best to match sizes and speeds but it is not an absolute.

http://www.techreaction.net/2012/06/...id-controller/