This is a no brainer - get the 40.1 if you must have one or the other. It can easily be used in a room like yours. Both designs share the same well regarded tweeter and are both considered excellent loudspeakers, but the 40 is naturally more excellent.
Furthermore all Harbeth speakers can be used near field and are voiced to sound good at low volumes.
However, however, just like @andysf asked above, I would also ask you to think carefully before pulling the trigger.
I’m far from certain that the Spatial X5s are so easily bettered.
Have you considered the possibility that your Spatial X5 speakers might even be better than the Harbeth 40.1s?
It’s certainly not impossible.
Isn’t it all too easy to sometimes denigrate what we have whilst pursuing something better?
Just yesterday I was playing a Smiths compilation on my Tannoys and it suddenly hit me, ’Wow, these are really good speakers!’
Maybe Morrissey’s voice and diction could have been a touch cleaner, maybe the speakers could have disappeared better leaving a ghost like sound behind, maybe the timbre could have been a hint more life-like, but yeah, pretty good.
Good enough to let me forget that I was listening to a recording.
At least for a while.
