A few weeks ago I discovered Mr. Robot. For those of you who don't know, it's a site that claims to help you optimize your gear and provides a list of BiS gear that's dynamic, changing as your other gear changes. While this is great, I don't think is accurately does this.
I also use WrathCalcs, and I think it's a lot more accurate. Now granted this is mostly my experience as a boomkin, but some of the values that Mr. Robot uses just don't make sense. It tells me that the Vibrant Alchemist Stone is significantly better than Theralion's Mirror, which is goofy. The stone gives a static 341 int (with gemming) and 194 haste bonus, where as TM gives 321 Int and 1926 mastery for 20 seconds every minute or so. If anything they just about break even. That's only one example. It also claims that the stone and the Witching Hourglass are significantly better than the Stump of Time, which is also ridiculous given my gear. I plug in the different trinkets to Wrathcalcs, and alter reforging so I stay hit capped, and it's a significant dps loss to equip either of those trinkets over the stump.
So basically what I'm saying is that you shouldn't rely on Mr. Robot for gear choices. It's difficult to tell what sort of formula they're using. With Wrathcalcs at least, they show you estimated dps based on your gear and stats, and talents. So you can see the numbers and understand them, instead of having just random numbers which have no significant meaning.