I have the earlier version of the SP3, the SP2 Signatures. They are in a rather large room, 26X16. They sound great, but I'm not sure how they would behave in your smallish room. I think perhaps the EPS would be a better match. My SP2s have pretty good bass output, so the SP3s might overload your room.
As for as quality of sound, the Montanas are pretty special. Not overly analytical or hyper detailed, but very dynamic and relaxed all at once. My SP2s will play as loudly as I care to listen with 100 watts of tube power without ever straining.
I think it would be well worth the time and effort to demo them in your own room. That is the only way to be really sure.
Good luck,
Oz