I really enjoyed your shootout and follow-up conversation. Thanks for taking the time to do the comparison and share your impressions!
I'm interested in the technical aspects of this last comment. What would a best-of-both-worlds speaker look like? Is it RAAL + Revel's midrange + multiple 8" woofers? I've read that Revel is known for their "driver integration", but I'm not entirely sure what this means (time alignment, crossover design, controlled directivity??). Is that an area where the Sierra tower could/should be improved?
I'm currently using a pair of Philharmonic BMR Monitors, which I'm extremely happy with, but I think my end game is a pair of towers. Like you, I run with a pair of subs so I haven't worried about low end extension or multiple woofers. But perhaps both are needed if you want the "fuller", "more impactful" sound you're describing?
Getting at the same question from a different direction... I wonder if Philharmonic's BMR Tower is basically the Sierra Tower XL you're describing.
As far as a best-of-both-worlds speaker, for me it would the Revel's mid-upper bass performance and larger soundstage combined with the sparkling, open naturalness of the Sierra's high end. For higher quality, well-mixed rock music like, say, Tool or Nine Inch Nails, the Revel's shine. The music sounds bigger and better balanced with more mid-bass thump and impact. The Sierras still sound largely great, but they lose a little bit of coherency and can tend towards more thin and shrill with certain tracks. The same is mostly true of big orchestral pieces. I definitely don't think a bunch of big drivers are needed. For me, the dual 6-1/2s on the F226Bes seem about perfect for my room. Some of that may be psychoacoustics combined with a bit of confirmation bias, but I don't feel that I'd gain much if anything in my room from bigger drivers than these (I had dual 8" Emotiva T2+ towers before).
I think the Sierras and Revels meet somewhere in the midrange, where both are absolutely excellent. From there they tend to best each other in opposing directions, at least with subs integrated. Again, I spent little time with them in full range. The Be tweeters are exemplary, and are probably the best I've heard outside of the RAALs, but they do take a back seat to the latter. I did listen to a few minutes of ~$30,000 B&W diamond speakers that absolutely knocked my socks off, but that was well over a decade ago, so who knows how I'd react now.
I gave a lot of consideration to the BMR towers. I opted against them for a few reasons:
They're not massive, but are a little bigger than I'd prefer for the space.
Their frequency extension and bass output are very impressive. I felt that this performance is a good chunk of what you're paying for and would be mostly wasted given the use of an 80Hz crossover.
There isn't really a matching center available. I suppose that a BMR Monitor might have worked, but it wouldn't have been an ideal solution in my setup.
I'm super impatient and there is a wait list for them.
Of course, having never heard them, you could be right and I may have missed out on my "perfect" speaker! I'd still love to hear them some day.