Whilst the subject of 'P' charts is s slight digression from thread topic. I'll throw in my two bits worth, based upon operational experience.
Slope limits is generally presented as +/- 2%; this being a typical day to day requirement. OEM electronic performance data, for biz jet aircraft will calculate within those parameters. So is Ops outside of +/- 2% not permitted? Absolutely not! The manufacturer has not tested the aircraft outside of +/- 2%. Special charts may be made available by request.
Answer is very simple; clear the individual runways with your insurance underwriter.
Scenario? Goroka in PNG, good slope, outside of 'slope' performace data, but the final acceptance is that the airfield is used by Fokker 70/100, Dash 8's of various models, previously Fokker F28 and even Fokker 27/50, turbo props. In my case the Underwriter was happy with the assessment as being 'sound' and CASA even accepted the argument as being sound (in writing) All take-off at Goroka are downhill, landings are all uphill.