Contagion takes care of IPS and Viral, mod for toxin radiation. You are welcome to try different mods, this seemed to be the best when others showed me this build.
Groll riven is DMG CD AS NEG
Attack speed is the most important as the contagion projectile speed scales off of attack speed.
NOTE: To proc viral you have to hit the profit taker in the side/back of the butt. Very hard t o proc consistently. To get more consistent with viral cycles lots of people use an On Call with [Tenet Cycron] to help out (secondary crit chance perk on Rail Jack Crew Member recommended).