I have used them. No issues but I know my guns. Your three frame will digest those loads no problem.
I thought too it was 8000 PSI but I saw this post by a gentleman from the Lefever Forum who sent some factory loads to Tom Armbrust. There are other shells you can buy with lower pressures and probably price per box cheaper. You have some other options.
http://lefeverforum.informe.com/viewtopic.php?t=1232
Bottom of first page is the chart.