sunnyjim, I think with most speakers of this type, Larsen, Ohm, Shahinian etc., you either like their presentation and get what the designers are trying to attempt, or not. They are different in various ways to direct firing speakers.
I have owned all of the above speakers, various Ohms, a couple of Shahinian, and also, Larsen Model 4.2's, which I had for over five years and enjoyed them greatly. I think Bill above, summed things up very nicely(Hello Bill, we have talked a couple of times, been awhile though!). Much like Ohm speakers, the family sound is there amongst all models, just as you go up the line, as Bill said, you just get more of it. Room size is important, just as much so with any speaker.
I totally enjoyed my time with the Larsen, and placing them as Bill mentioned above, try to keep them from being crammed into corners, and give them a bit of space to breathe on all sides, they are hard to beat for just listening to music and enjoying, no fiddling around etc. For me, this was huge, for once I had a speaker that I could just forget about messing around with things, they made great music, simply put.
I have never had a pair of speakers for five years, let alone a bit longer, so that is saying something. I cannot answer your question as to the "worth" of the model 6 over the 4, at the additional 2K price. Only you can make that call using your own ears. I also wondered that myself for awhile, as I was thinking of moving up the Larsen ladder at one point. But I never bothered, as the 4.2 I had were just doing the business and I had no real reason to change them.
One thing about Larsen in general, they are not, nor ever will be the popular choice. I have had other dealers basically make fun of them to my face, and try to explain why they are not a good speaker etc. Yes, really. Thank goodness then I never listened to their advice. Funny how that goes though. But, if you like what they do in your room, your gear, your music, why not? For people that require a speaker that goes up against the wall, and do not have room for some of the speakers that require huge room space, these are great speakers to try. They visually get out of the way, give you your floor space back, and to my ears, sound quite wonderful. Are they the last thing on detail, imaging, all the usual buzz words. No, maybe not, but what they do is really very good across the board, besides, I listen to music, not buzz words. Take it for whatever it is.
In the end, it took a good deal bit to get me away from the Larsen 4.2, and I listened a lot to other speakers. I think in the end, it was more of a system thing, and not just speakers themselves, so don't make the mistake of not listening to speakers on your own setup, it is after all a "system". I now have a pair of Duevel Venus speakers, and yes, I like them more than the Larsen 4.2 in a few ways, but honestly, I too could have lived on with the Larsen had I not changed my entire system a bit over a year ago. This will probably be it, at my age, and time of my life, other things have more priority.
If you can though, give yourself a treat, give the Larsen a good listen, just do not give up on them too quickly, which I find is what happens all too often when people try Omni or Omni types, they do present things in a different way, and many will not allow themselves time to adjust to it. Not to mention, I think the industry has not done much to persuade a person to try this type of speaker, instead giving the same old reasoning: Look at all the box speakers out there, how can we be wrong? Omni's are just a fad, a one-trick pony, etc... etc....The main thing, use your ears, not reviews, not my suggestions, or anyone else's for that matter. And for goodness sakes, anyone trying to listen to speakers out there, have fun darn it! It isn't life or death, music can be fun!!!!