I have the exact same setup (M22's, VP100, and QS4's) as you described.

Seems like you're already set on the center.

I just wanted to chime in saying that while I am happy with my setup, you should definitely go for the QS8's.

Check out this review that I conducted some time ago, where I compared the QS4's vs QS8's:

Good luck with your decision!

M22s|VP100|QS4s|HSU STF2