I like my os , sonar, project files and vst's on one drive.
sample libs on the other.
you can always use on hd and take your projects to an external or second HD.
imo theres no need to have more than 10 project files (CWP) on one HD.
if you need more 20 tops. anymore than that,swap them out.
I never have more than 25/30 GB of projects on one hd.