I reforged all my gear (pvp) and got up to something like 15.63 mastery or the likes. On the test dummies, I didn't see any increase in DPS - seeing a solid 8500 DPS for both configurations. I think in the end, I lost something around 8% crit. For BGs, I can't say I really notice a difference, except on the pillar humping LOSers. If you manage to get one spell off on them, there's a very good chance, they'll get hit again from overload.