Who has the math?

What is more impactful?

both help separately from each other, so the boni are multiplicative. keep in mind that plr in hell is -100 per default (as for every other resist)

stack is only needed if there's a source that will reduce poison resist, such -poison resist on gear or lower resist curse.

The math is really straight forward..

If you don't know how resistances work just think about it.. If something is 90% resistant, only 10% of the damage will be received.

Then factor in 1/6 PVP penalty for damage

then factor in -100 PLR in hell (With 0 %PLR build, this will mean doubling the duration and therefore the damage.)

Venom is such a short duration that we can just ignore the duration factor and consider it all damage.

damage received = (Damage/6)*(1-(PLR/100)*(1-(Resistances/100)

Plug in your values and figure it out yourself