How good are the Harbeth 40's?

Well, the Harbeth website recommends 100-250 watt amps. They were designed as a "drop-in" replacement for a large BBC monitor, and as a professional monitor, probably unequaled. Very few people have them in their homes and it seems like 3 of them have them up for sale. They are very large, and with a 12 inch woofer, difficult to situate in a real world room. They are the favorite speakers of Robert E Greene (REG), the longtime speaker reviwer for The Absolute Sound (TAS). Though they are listed below a lot of more expensive speakers on TAS's recommended list, REG says they are demonstrably better than almost all (maybe all) the more expensive speakers listed ahead of them.

I don't think your room is big enough for them.

The 40's are an excellent speaker. I've heard them in room sizes very similar to yours, and driven by amps in the 60 to 70 watt range, with great results. I've also recently listened to them driven by the big 200 watt Pass amp, most impressive!
Paulwp is right, they are big and may be difficult to place comfortably in the average living room. If your room is dedicated, 22 feet deep is great, while 14 wide would require some tinkering. Around 8 feet apart is good for the 40's, and that still gives you 3 feet out from the side walls.
My room is dedicated, a dreaded square 14x14. I have the Monitor 30's ( love them! ) and with an extra 8 feet of room length to play with, and some spare cash, would have the 40's in for a listen tomorrow. Its difficult to consider gear if access for demos is not available, but I know that many music lovers have bought Harbeths, including 40's, without hearing them, and have no regrets. They are that good, IMO !
Good luck,
Mike

Emster:

One of the people you might want to contact about Harbeth speakers is Charlie, one of the Audiogon "oldtimers". Charlie owns Harbeth speakers, and he corresponds regularly with a goodly number of other Harbeth owners. Charlie's user name here on Audiogon, as I recall, is "Danvetc". Charlie is a great guy, and I'm sure he'd be glad to offer an informed response to your post.

Sdcampbell, thanks a lot. I have sent Charlie an email and will keep you up to date. Thanks also to Mike and paulwp.