What functionality is lost without LTE? According to Apple, A1660 and A1661 cannot do LTE in most of the world.  My experience suggests that many functions are unpleasantly slow or even impossible without LTE.  But I haven't been able to find an A1784 or A1778 in Oregon or on the Apple website.

Contacted Apple and got an "expert" who insisted the A1661 works anywhere in the world and seemed to think that web page was inaccurate.

Online descriptions of LTE suggest that there is no hard-and-fast number to describe its bit-rate.

A related question suggests that I would not be happy with the CDMA choice, and the Apple page seems to say that for it  to work in Japan, I have to buy a model that is crippled anywhere else.  

If I get a CDMA iPhone 7, is there a reliable description of what kinds of apps will not work in Mexico City or Toronto or Madrid or Seoul or similar places?
Yes. 

Every iPhone has enough GSM frequencies to work with any carrier that wants to provide service and/or bill you international roaming. 

Of course, in bad coverage areas, higher frequency signals are much shorter range so the traditional CDMA frequencies work better in rural areas. 

With 250 plus carriers in 150 countries, you’ll always have some pain in some places, but an iPhone that’s still in Apple support is basically a universal communicator for social, monetary and technical reasons. 

And in fact, after looking closer at the Apple page cited, we can see that the four models OP mentioned have exactly the same 41 bands.