Which Harbeth would work in my room?

Your big task is going to be getting the speakers out from the 'front wall' yet not having them too close to your listening spot.  Very few speakers perform well against the wall and Harbeths in particular are noted for loving free space. 

Off the cuff, I think it's possible that the 40.x models may be too much speaker for your application.  The SHL5+ and 30.x might be right, and I'd consider the C7 models as well.  So far I've only listened extensively to the C7s in a semi-near-field setup (around five or six feet away) and my 30.1s have just arrived.

This means (among other things) that though I may be first to answer, you'll probably get more comprehensive replies before too long.  I will say that the Harbeth C7s have been hypnotic.  I'm obviously hooked which is why I've purchased a second pair (the 30.1s).  It'll be hard for you to go far wrong.

I have 40.2 Anniversary's now, and previously had 40.1's.  Prior to that I had 30's.  I was worried about the 40's being too big for my room (12' x 14') but I like the 40's better than the 30's, even in my relatively small space.
I have the speakers set up about two feet from the back wall and two feet from the side walls as well.  My listening chair is 7.5 feet from the speakers.  This is close to near field, and I like this presentation.  
I have had my 40's set up in my living room for a while.  I enjoyed them in a larger room but I still enjoy them more in my listening room.  
The 30.1's are amazing speakers but I had to add a subwoofer to be fully satisfied.  The 40's have never needed a sub.  
I have not heard the C7's but I don't hear the rave reviews for those as much as the 30's and 40's.  This is not to say that you shouldn't consider them, but if you're buying speakers without auditioning you might go with one of the models that seem more universally loved. 
You might want to call Gene Rubin Audio and ask Gene for advice.  He has heard all of the Harbeth speakers and can speak with authority on this topic.  Cheers