Harbeth 30.1 or 40.1

@gte357s 
My amp was a Lyngdorf TDAI3400 when I got the speakers but after that I tried an LFD NCSE 3 and prefer it.  It’s a solid state amp that sounds more like tubes.  Great amp, but very simple, and lacks the convenience features of most amps, most notably a remote control.  My second favorite amp with these speakers is the Primaluna EVO 400.  I might buy one in the future as a second amp because it’s really that good.  

@gte357sI ran a 4 sub array with my SHL5+40ths in a small room (10x12 minus closets).
The sub array really helped.
Now I am in a bigger listening room (14 x 17) and the SHL5+40ths really opened up at louder volumes.The sub array really helped in this room as well.

I have not heard the M40.1 or 2 but can vouch for the SHL5s.They fill the room without effort.
Seems like an even bigger room will let them play more into their "sweet spot".
I would strongly suggest considering the SHL5s and using the extra cash on a subwoofer solution.

@gt357s

mon 30 are midrange oriented monitor more for semi nearfield listening - will need bass reinforcement if run full range deliver dbs into 18x16 room

mon 40.1 are very full range, perhaps overly so... i had mon 40.1 before, they boomed, need to be far away from room boundaries - have you seen these speakers in the flesh?  they are huge boxes, know what u will be getting, if this is anything but a dedicated sound room there may be aesthetics issues

otoh, the c7 and shl5 bridge the gap between the two - c7 small box but more balanced high thru low, shl5 basically a larger version of c7 with supertweeter, similar voicing - 18x16 is good size but how will you set up the triangle, how close to room boundaries and therefore how much bass reinforcement?

Yes I have only heard 40.2 set up in large room away from walls. In smaller room closer to walls or corner with more bass reinforcement from the room I might be concerned going in about too much bass and no way to tame it other than eq or tone controls., which is always an option. They are big! “Full range” speakers in a smaller room is not always a good thing.
Something to be aware of. Too much bass can be detrimental to the overall sound, obscuring the otherwise lovely midrange and detail, and very hard to tame.

Vu of Deja Vu, who's a major Harbeth dealer, stated to me that the 40.2's needed 2' of clearance from side walls and 3' of clearance from front wall (behind them), all measured from the relevant edge of the cabinet.  The experience of the gentlemen in the link I posted earlier suggests that you can get away with less and still get very satisfying sound.