[werk_ag]

I had success running a SHT15 temp/hum sensor using a 20 (twenty) meters long cable (4 x 0,22mm2).

That's another interesting test.

In practice I am not planning to use more that 2-3 meters. Still, the "5 meters maximum length" is perhaps on the conservative side. Which I reckon is always a good starting point.

Indeed, the SHT1X (when powered by 5V) and the DHT22 can be used with very long cables. And you are right, most of the time I give very conservative specs, this way I'm sure things will work in any circumstances.