Hmm. In my experience with the Beolab 90, increasing dispersion (which can be manipulated) did increase the width of the soundstage but at the expense of detail, imaging and specificity.
Interesting, and that's probably the perfect speaker to test with. Your experiences exactly match my own. My narrow dispersion(60° beamwidth) speakers have by far the best imaging and clarity. My Revels have the widest soundstage of any speaker I own. The Revel's imaging is the least precise, but, not by much, and I find they have an overall excellent balance between image precision and soundstage width.
Perhaps there are optimal values, depending on room dimensions and boundaries.
I tend to think there is, but I also think it depends on the listener, as well as the number of speakers. As the number of speakers decreases, the advantage of wider dispersion increases. Did you get a chance to test the Beolab in mono? I wonder if the wide or omni modes might be preferred over the narrow for mono single speaker listening?
For stereo, I find my 8351s probably strike the best balance of soundstage width and imaging, followed by the Revels(I don't have TOL Revel's like you). The image specificity and clarity of the 60° JTRs is intoxicating in it's own way, but the width is lesser. For reference, looking at reviews here, specifically at 2-10kHz and the -6dB point:
Genelec 8351b: ~100°
JBL 708p: ~100°
Revel F328Be: ~100-140° (140 most of the way)
Focal Solo Be: ~140-180°
Neumann KH310: ~95-105°
KEF R3: ~80-100°
From memory(you can correct me if I'm wrong, and I'll edit the post), the narrow, wide, omni options for the Beolab90 were 100(or 110)° , 180° , and 360°, respectively.
The Genelec and JBL stand out for being near perfect in terms of consistency, but not as wide as some of the others. The interesting one to me is the Revel vs KEF comparison, as I see them as competitors. They're similarly neutral, so it's nice to have well designed wider and narrower option in the passive market. Might also have something to do with the target audience, as well. I would expect KEF to throw a more precise center image(especially with coax), and the Revel to throw a wider soundstage.
I think the Genelecs are ~105-110°, Revels are ~130-140°, Focals (less even, but wider in that soundstage portion) ~120-180.
P.S.: To answer the question in the thread title, I have not yet heard any speaker with a wider soundstage in my listening room.
Only thing I've heard that's wider than Revels is the big MBLs at a show, but I found that they sacrificed too much in the imaging department. I know
@echopraxia had an Revel F206 and Ascend Sierra Tower at the same time, and the Ascend was (IIRC) preferred in a blind test
, due in part to the wider horizontal soundstage. I'm really looking forward to seeing spins and beamwidth charts for the Philharmonic BMR Tower, that thing could be a real steal for wide dispersion lovers if it does well.