Good point. I do know that I'm trying to thread a tight needle with this, which is why I posted in the first place - if it was easy it would be easy!
When all is said and done I could drop my sensitivity requirement and use a different amp for playing live in this group, but if I don't have to that would be cool. I have a huge Bag End S15B-D 2x15 cab (I think that's the model - it's the bigger enclosure) that I can use at home with the low power head and it takes care of business. But, as is being pointed out, the cab is very large to get that sensitivity. I really don't have to play very loud with the low power head, but I want to squeeze what I can out if possible.
I can also be pretty flexible with the size - I'm not looking for the smallest, just reasonable. However, if the size/weight starts approaching what I already use then other attributes would have to be that much more superior to convince that the change is needed. After all, I'm generally ok with the 2 Yorkville 15" cabs. I probably could simply spin the bottom one towards the drummer (as was suggested in an earlier post). Sure, it's a lot to haul, but I don't gig that much.
I will probably not utilize a tweeter, but some of these systems with arrays of smaller mid drivers seem attractive.
Thanks again everyone, a very enlightening thread (for me, anyway)
When you stack HF drivers vertically, you narrow the sound in the vertical plane. The good thing about that is that you minimize reflections off the floor. The bad thing is that it doesn't sound as open. The vertical pattern control is created by the comb filtering (destructive interference) of the stacked drivers.