I remember before I got those talents my Doom accounted for like 8% of total damage, then I tested on dummies and doom double proc chance happened to be around 25%(not sure). So I would say Doom double around 2%, 3/3 DoA around 2.5% but both talents have great synergdue to the face that Doom can now proc 4x dmg and that's a huge dps spike if it happens, so definitely more than 2+2.5=4.5(Also It comes with Huge RNG and that could be frustrating in some times, my doom average damage is anywhere from 350k to 600k)