Hi,
I think you'll be sitting back far enough, and the vaulted ceiling will nicely add to the ambient mix of reflected sounds, so you'll be fine with the M60ti's. You should be able to achieve very good imaging and a realistic soundstage with that setup, even though they're just five feet apart.
By the way, if there are clear side wall surfaces (not bookcases filled with stuff) to the left and right (your left and right as you face the speakers), that can enhance the "spaciousness" of the sound from the M60's because they have very smooth off-axis dispersion (to either side).
Regards,
