I might think about it in terms of cost per hour of use. The typical american keeps a phone for about 2.5 years and uses it for about 5 hours per day. If you last bought a phone in 2017, it sounds like you keep your handsets for about 2x as long as the typical person, so let's say ~9,000 hours of screen time. That would put the base sized 14 Pro Max at about 12 cents per hour of use. The 14 Plus, on the other hand, would be about 10 cents an hour of use.

So the question is, are the other Pro Max features like a better camera worth 2 cents per hour to you? Based only on size and battery life preferences, PerfectRec has the 14 ProMax at a 59% match and the 14 Plus at a 52% match for you (results), which is pretty close. If you can still find a 13 PM at a local retailer, that might be a happy medium. But the big picture is that if you're getting a ton of life expectancy out of your phones, the incremental cost between the Plus and PM isn't that much.