Let's say I'm wearing trangs for their +25% to psn skill.
This get's me the bonus on cast of: 1085 x 1.25 = 1356 over .4 sec
And the bonus on application of: 1356 x 1.25 = 1695 over .4 sec
Finally, add in the hell poison length reduction penalty of -100%.
This get's me: 3390 over .8 seconds
Now figure the 1/6 PvP penalty: 3390/6 = 565 actual pvp psn damage over .8 sec for each application
Assume 75% res (generous since most people tend to somewhat neglect psn...): 565 x .25 = 141 psn damage over .8 seconds
So, level 40 venom get's me 141 psn damage in hell vs. someone with 75% res., basically per application, even if kicking/whirlwinding (since you don't land all your kicks/ww's/etc. due to chance-to-hit, block, etc.). This number obviously goes up dramatically as enemy psn res goes down.
It's the same all around. Feel free to do testing. (Btw, big fan of your WW tests.)
My hunch is that the 1/4 is either old news from .09, or the PLR penalty in NM/Hell threw off the testing. The PLR penalty is the same as the resistance penalty in both. That is why the damage and length were doubled for Hell.