A good friend bought a pair of M60s and a pair of M3s for another room, so I had a chance to listen to both side by side (without a sub for the bookshelves).
While the M3s are amazing speakers, at louder levels they started to sound a bit strained were the M60s did not; that being said, for my friend's setup they are perfect as they would not be driven to high levels.
I guess it comes down to what your listening preferences are and no doubt that with the addition of a sub, bookshelves can be very good choice.

M80 v3, 2 x Emotiva UPA-1 Monoblocks, XPA-5, UMC-1 PrePro
Pro-Ject RPM Genie, Carver C2 Phono Preamp