MBL 120 vs 126

I had the 121s in a 13' x 15' room.  They are in between the 120/126 in terms of size/frequency response.  They worked great in my room.  Though I do have a fairly wide opening in to a hallway which helps with bass I think.

11' x 11' might be pushing it with the 120s, unless perhaps you have a lot of flexibility for placement.   The stereophile measurements show quite a boosted bass even, as JA says, taking in to account the usual hump in his measurements:

https://www.stereophile.com/content/mbl-radialstrahler-120-loudspeaker-measurements

So that could be challenging.

Hard to say.  The stereophile review quoted MBL as saying the 120 is particularly flexible in working in different rooms.  So maybe your small room would work.

Does it work to go with the model you prefer, and then just see which room it works in?

I've actually kept my eye on the used market regarding the 120.  I've thought if I ever wanted MBL again that would be the one - an updated version of the 121, that also goes deeper in the bass.   Though really that's a pipe dream for me at this point.

But the 120s are very rare on the market.  I notice though there is one for sale on stereonet right now:

https://www.stereonet.com/forums/topic/577622-mbl-radialstrahler-120-loudspeaker/