[brucepick]

From reading the "police" article I gathered that handling improves with pressure. That would be due to the sidewalls stiffening up with increased pressure.

Steering response definitely seems to improve; I found it got noticeably lighter once I took the pressure past 44 psi to around 50. It let me disable the power steering. My 3070 lb. car handles well and is not too heavy to control with the tires at 50-52 psi.

However, I dove off topic above.
I'm trying to steer back to the brake traction test.

Reason is, I think this is the one most critical safety need. And the one most often quoted as a reason to stay with the "manufacturer spec'd" pressure. It's also probably easier to measure than handling.

Just do a straight line stop from any given standard speed and measure the length of skid marks. ABS will pulse the brakes for a standardized optimum efficiency. It should give a strong indication of basic dry traction.

As to hydroplaning, I think the "police" article shows pretty well that hydroplaning is avoided better at higher pressures. We could test for that but again, it's more of a special purpose condition. As would be a snow traction test.