What you want to do is download SimulationCraft from this link:
http://downloads.simulationcraft.org/?C=M;O=D|
I can assure you that this is safe, but of course
don't download it unless you're willing to.
Also install addon "Simulationcraft" from curse
Then, go to options in Simulationcraft program. Set fight length to the one you're interested about like 150s or whatever. Set up Iterations to whatever, the more the less RNG. Set up player's skill to Elite or Good.
Launch wow client, log to your char, type in /simc in chat and CTRL+C copy everything and CTRL+V it into Simulationcraft's program "Simulate" section. Then press simulate.
You'll see result, for example 313k DPS.
Then change trinkets to the other one(s), type in /simc again, copy everything, paste everything to Simulate section and simulate it again.
Simulations are reliable