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I know that even treadwear is critical on awd because it can cause binding on the drivetrain. Is there any reason why you shouldn't run max sidewall with AWD provided all 4 match?

I think it's ok if you match them. Check the manual and see if it recommends the same pressure for all 4. If not, you should probably keep the same ratio front to back while raising the pressure in all. (eg 32 front 36 rear, pump up to 42 front and 46 rear)

As a Subaru driver, running at or near max sidewall since June, I know of no AWD issue with this pressure. My rear suspension is complaining, but that is likely caused by age (12 years) and some past roughness, and only highlighted by full pressure. But the summer tires seem to like it. I had expected to reach my wet traction dissatisfaction level by now, but with the past 9k miles on them at full pressure, they are still good enough to start the coming summer, with not even any hints of wet traction problems. The tread wear is actually more even now than last June, as the subsequent full pressure has put new wear onto the thicker center tread, away from the shoulders thinned by previous driving at placard pressure.

I disagree with calling the sidewall pressure "excessive", as in this thread's title. My tire ratings actually require this pressure if the tires are operated at full rated load, though that load would seriously overload the car itself.

Title changed. Below the sidewall rating is within the tire manufacturer's specifications, and therefore not excessive.

Whatever the Pressure!
Just keep all the same pressure in ALL!

High or low are OK, just NOT difrent.

Different pressures will create diameter differences, causing different wheel speeds. Those differences over a long time will do damage to many AWD systems.

Trucks with duel tires will often have one tire blow out if the pressure is not close between the two tires. Happens a LOT. and it's the low psi tire that fails.
The tires are bolted together and there for MUST spin at the same speed, but there different diameters means they don’t cover the same amount of distance with each revolution. Something has to give, one tire constantly slips a small amount, causing heat, causing tire failure.

Same thing in an AWD, the drive train wants all tires to turn the same speed. If the speed differences in at each wheel drastic enough something will eventually fail early.

In some cases like my crossover I found higher in front lower in back gave me more stability.

I run 40 all 4 in my CR-V. They are rated at 44 lbs cold. Michelin Hydro edge. Hal

Thanks to all for the replies. I apologize for the misleading original title. Sometimes you think one thing and write another:)

Just to clarify my earlier post. If, like my car, the weight is not evenly distributed, you get a different amount of "squish" on the front tires compared to the rears. That changes the revs per mile. So they are compensated with more or less pressure compared to the rears. You want to maintain this.