Harbeth 30.1 or 40.1


I would like to get a pair of Harbeth, and wondering if 30.1 or 40.1 is better.  My room size is about 18’ x 16’.  I currently have a pair of Spatial Audio X5 with large 12” mid range driver.  I would say I listen in low to low-medium volume for Jazz and vocals.  Is 40.1 too big for my area?  I am afraid if I am not listening to what it is supposed to sound like if I don’t turn up the volume.

however, if I buy the 30.1, is that I should get a pair of sub?  Versus for 40.1, I assumed I don’t need subs?
gte357s
@jond how would you describe the difference?  I never own a monitor speaker, all my speakers are full range speakers.  But then recently, I feel they are actually a bit too big for me.  I realize they sound better when I turn up the volume, but then it is too loud to my taste.  Is there such a thing as optimum listening volume for different speakers?
gte357 to me there is an optimum listening volume for each piece of music not so much for each speaker. To my ears the difference between the two is the 30.1 images a bit more precisely but the images don't have the density of the 40.1. Also you get more sense of the room the music was recorded in with the 40.1 because of their much deeper bass. The 40.1 is much deeper in the bass but a tad less airy on top. Both speakers have a top notch midrange detailed and transparent with natural warmth. 

When you say the 40.1 has much deeper bass, does it need a louder volume to bring it out?  Or they are at similar volume?
40.1 seem designed for larger rooms and yes far out from walls. 

I’d start with the smaller Harbeths in that room.

Buy used and don’t overpay or buy new with return policy if you want to keep your options open.