https://townfairtire.com/information/tire-information-guide/what-does-utqg-mean/index.shtml
I am not sure on the Continentals whether they are built that way or during some inspection there are some tires that are better than others? I don't know. But a higher speed rated tire is almost always a better built tire vs. a lower speed rated tire.
E-load rated tires can easily run at 40 psi.
My 16 Outdoorsman came from Ram with E-load Goodyears on it and the rec. psi is 43 psi on the door post. Light won't turn on until the pressure drops below 36 psi.
I had a 17" version of the E-load Defenders and ran the pressure from 38-40 psi up to as high as 70 psi.
They surprisingly didn't ride bad even at 70 psi. and that was with the HD rear springs that were rated at 50% more capacity than stock. 20's would probably ride a bit firmer than the 17" at 70 psi