Todd,

RE Never heard of a 251J and don't see specs on it anywhere

Haven't found any either, surprising since its a "named" JBL driver with model number and sticker, not an oem type having only a part number.

RE Crossing the Heil over at 1kHz is a mistake.

I agree, based on Eargle's Loudspeaker Handbook showing a late 1998 MLSSA response graph for the Heil (don't know which version). At about 1khz its down 5db, 1.3khz up 4 db, say 1.5khz down 5 db, and at 1.7khz or so its back up on the line for good. So below 1.7 khz its a rather "bumpy ride". However, from that last frequency its pretty flat (but for 2db peak at 18-19 khz) out to 20khz where it rolls-off sharply. Off-axis curves are also given but the applicable angles are not mentioned. Often such angles might be 15/30° or 30/45°, pick the one you think fits best according to your own experiments. Anyhow the worst case response shown for off-axis is about 3 db down near the top end. Not bad!

RE Still, there are those that would say that this is too high a frequency for a ~10" speaker based on the wavelength.

Well, based on Weems' speaker building book the upper limit for a 10" is 1.5 khz. As for Eargle's, its a little more detailed: with a Di 6db (the usual standard) its 1100 hz, but stretching it to Di 10db then its 1650 hz. So at 2,150 hz its somewhat high but since you mention always sit in the sweet spot, then the actually more directional 10" is being less noticed i guess.

Don't worry i'm a "cheater" too. Having a pair of boxes with a 10" (special cone for warmer sound) along with a horn tweeter which can be crossed over as low as 1.5khz, but actually done about 2khz for little increased power. That one isn't a hi-fi style box, rather a small sound reinforcement one i can biamp with the 2205H cabs for noise making, or simply use it as stand alone, like a "side fill". In my case the more directional woofer is matched with a more directional horn tweeter, so reduced driver coverage pattern issue.

As a separate note, i'm surprised following your post, as well as Widget's, that nobody mentioned the McCauley 6222 the OP has shown, maybe its outside the comfort zone? I quickly checked it before, having their catalog within arms reach, and saw some potential there (needing confirmation as usual), and depending on how/where he decides to go. Unfortunately this doesn't mean i magically have more time available.

Richard