Nathan, I think I'd have a hard time going from M80's to a smaller speaker. However I do have the M22 in/on wall (now discontinued but it's like the in walls and on walls combined) and I do think they sound great with a good sub.

What about doing wall mounted bookshelf speakers instead of the on walls?

I would not recommend vertical VP150's. They are designed for horizontal placement.
On-Wall M5HP LCR, QS8 & EP500 in 7.1