MacPro5,1 Best SW Raid config?

Hi Folks,
As I just ordered a Crucial M4 512GB I thought I might reconfigure my 2 HDs currently set to SW Raid0 that I was using as my boot drive.

Can I (or should I) run SW Raid5? I can shove a couple of more HDs in there similar to the 2 already in it and Raid5 them all?

Thanks for your help as always!