Well, I don't have a ton of experience, but I've gone through several chokes in my pursuits and chasing patterns. And you're right, patterning is the only sure way to find out.
The reason I believe the .660 is too open, is a good deal of predator hunters using a 12 gauge, consider that exit diameter to be the starting point for loads as big as #4 buck in something like a 3" shell with 41 pellets.
I like my Carlson's coyote choke. It's the nearly the same exit diameter as some of the more open turkey chokes (like those listed in the area of .660) It works best for me with heavy weight B shot but it's nearly the same with 4 buck.
The Carlson's LongBeard isn't a bad choke, but at least in my case, I couldn't reproduce the patterns they boasted. Perhaps at closer range maybe. I really feel the .660 is too open but if you try that and then maybe pick up a couple chokes from eBay, it may be worth it. I check eBay from time to time looking for stuff I haven't tried before and it's a more reasonably priced alternative when you aren't sure which way to go.
I'll echo something I mentioned briefly before, if you're looking for a long shot, the #6 with a tighter choke may be the way to go. If you think you're longest shot will be inside say 35 yards, (most shots are I believe) then you may not need that much choke.
Ultimately, I can only offer my personal experiences and agree with you 100% that patterning will have the final say.