Correct FrankD, I went with the 4 driver / full size version. Even at full size, these things are very compact. I can't imagine how small the 4" version must be in real life. That might be an option for your delay stack as well - that would certainly reduce the "visibility" impact on your congregation.
I ended up going with the Eminence Alpha 6(a) drivers.
I was on the fence and just about to pull the trigger on the much less expensive Dayton Audio's, but Parts Express ran a sale on the Alpha's about a week before I was ready to build and a vendor I had a credit with honored a price match, so I went ahead with the Eminence. I wanted to do the new Alphalite's, but my timeframe and budget dictated otherwise. I'm very happy with what I ended up with.
The Alpha's at the sale price made my driver investment about double the Daytons, but I do like to stay with recommended drivers when possible.
Had I gone with the Dayton's, I was going to incorporate a 12db low-pass filter around 3.5k to try to tame their 5k rise that the Eminence's don't have.
I was also worried about the lack of xmax info on the Dayton option, but now after hearing these and realizing that they do pretty much NOTHING below 100Hz, I'm not sure that is an issue - just high pass at 100 and I'm sure they would be fine.
In fact, at one event I ran them up to about 120/130 and my T39's low pass down to about 70 and got quite a pleasing sound in that particular venue (playing pre-recorded music.)
Since Bill chimed in with the great animation on dispersion, I won't go into detail - but suffice it to say these have done just fine in both long/skinny halls and the short/wide auditorium I was in this weekend. There was a nice and wide sweet spot in the auditorium. That being said, I do think I want to build a 2x6" version to do the stacking with the short ones on the bottom of the stack and turned inward as has been mentioned to create a "best of both worlds" situation with wide coverage for the close audience and long-throw for those in the rear.