Speaker Distortion or Room Interaction ?

my floor-standing speakers are quite powerful already, and sound very clean up to a certain (fairly loud but not party-loud) volume. BUT past
that, the sound starts becoming increasingly smeared and eventually becomes harsh and unlistenable, probably due to room reflections, but i have no way of measuring speaker-distortion levels like they do in stereophile. my room does
have some reverberation issues, which i've treated with echo-busters to good effect (although the room is still far from "dead"). but this is my living room also, so i really don't want to add any more room treatments. at the same time i've been seriously looking at even bigger speakers for a few years to get more resolution, sonority, and headroom in the low bass dept. in other words, i dream of listening to large-scale works of music at more realistic volume levels with a minimum of distortion. SO, the question is, if i go ahead with an upgrade, am i going to run into the same problem, or possibly even encounter worse room interactions?
or would a larger speaker sound so much better at a more controlled/lower volume level that it would be worth it for that alone? i know what some of you are thinking- build a dedicated listening room, otherwise the dream of recreating beethoven #5 will forever elude me.