Bruce,
Well stated! While Parker barrels in good condition should withstand high pressure loads the stock will be damaged. I think the action will certainly also loosen after a diet of 8500-11000 PSI loads! The steel grades of 1890 were not what we have today.
From personal experiance, this early season I took 5 geese using 1 & 1/8 oz of Nice Shot #2 at 1200 FPS and 7000 PSI. I dropped two of those geese at 50 yards. I think that I need to load some 1 & 1/4 oz Nice Shot for my Parker 10 gauges! One never knows when a 60 yard shot will be needed..
Good shooting to all! Keep the pressure down and you'll be able to pass on your Parkers to the next generation!
Respectfully,
Mark