10psi tire pressure makes a difference...

[Flanders]

...Your pdf link - to Toyo tires has a graph that is very close to linear, which validates my thinking;

I wouldn't say that. Here's what you calculated for your original (non-P) 245/75R17 tire vs the ETRTO load limits.

You could avoid the hassle of downtown Wrongville by skipping the footprint nonsense. You're assuming load limit is linear in pressure, i.e., load limit = 2469 * pressure / 45.

If you actually read the Toyo pdf you'll find how they got to 49 psi for your LT245/75R17. It's not what you think*. Here's the chart for this tire vs your estimate again.

*The stock tire has a load limit of 2469 lbs at 36 psi. It's a non-LT tire on a light truck so that's derated by 10%. For the new LT tire of the same size we're looking for a load limit of 2469 / 110% = 2245 lbs. The TRA Load Inflation Table shows a load limit of 2270@50 and 2110@45. Interpolate to get the recommended inflation of 49.2 psi.

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[Pilsner]

I run my MT MTZs at 26-28 cold and 12ish offroad. I have run them down to about 6 or 8 when needed on Method Beadgrips.

ETA: 37x12.50s