Back when I ran a load of reforge plots a couple weeks ago, the sweet spot I found (which was my initial reforge anyway) was Mastery > Haste=Crit.
I had like 15.5k mastery and 7.5k Haste/Crit. Reforging either way caused me to lose dps. Definitely believe the 2 stats scale in synergy with each other, much like haste and mastery for affliction.
Sine I picked up BBoY and HC Bindings the stat weights have shifted in favour of haste, but I haven't had time to run any plots as of yet. Will go do so now and see what comes of it.