I would like someone defining large room vs small room in term of physical size. Large vs small is very subjective...
I have my Vantages in an attic room, 14 x 24 x 8 with (sloping walls) and they sound superb. I would characterize this as a medium-sized room. SPLs and soundstaging width/height are abundant as is the dynamic character of the music -- NOT the case with the (highly-regarded) floorstanders that the Vantages replaced. In this case there's no substitute for listening but the price differential between the two models is substantial and larger speakers do need larger spaces to work properly. I appreciate the capabilities of the Summits, though I can't afford them, but having listened to both I don't feel that the Summits "demolish" the Vantages; they have a little more space, scale, bass weight and control and dynamic freedom but -- and please don't flame me for this -- I'm not sure they're as coherent-sounding as their little brothers and they seem to lack a bit of midrange warmth in comparison. So, in a sympathetic system and a smaller room, I can imagine someone being happier with Vantages, which are considered to be (and reviewed as) reference-class loudspeakers. They are NOT the Summit's poor relation but an excellent design in their own right. IMHO, anyway. Your space sounds like it would fit either of these Logans -- I would absolutely try and arrange a home demo before shelling out.
best,
k