Now of course most airports are 2% or below...
That’s the real kicker for “rules of thumb”. If you are sitting on a runway with a 4% slope, you’re going to know it, and it’ll be obvious the slope wins.
That’s not a small slope even if “4%” as a number looks small to our brains in text.
Would be interesting to have an easily accessible database where a query could be done of public runways with a slope above 2%. I don’t think you’re going to find a whole lot of them.
I don’t know of any way to query the public FAA data for that one.
Sparky operated off of some very interesting strips, especially after he left here and moved to Idaho. Probably the one place in the US that has way more than average numbers of oddball slopes on public strips. Alaska too, I suppose? Not all that common anywhere else though.
And of course you know this, but folks from some areas never see them, a lot of the “one way” airports and strips out West here are not because of slope, but because there’s a big fat mountain at one end of them.
Terrain dictates the in and out end of the runway, since you can’t out-climb the big rock in the way.
Many are also “iffy” going one way and “nice” the other, which is how my mind read the data for the OPs original airport in question...
Slope, obstacle at one end, displaced threshold, and an odd ball approach angle all listed for going that downhill direction, all indicated caution, but wasn’t as big a deal as a 14,000’+ MSL mountain staring at you off of the departure end.