Running double Amp trinket (healer and dps) i am at like 105% mastery (can reforge some off), in town, always on. I am gemmed nearly full mastery tho. Was more of a proof of concept. Did use double amp on the bosses today on ptr, and wow, the damage was ridiculous. I was able to proc both trinkets together nearly every time within 10 seconds of pull, and they lasted the whole duration of ascendance. I cant see these trinkets going live atleast not without making them unique. With banner i was pushing out ~1 mil damage every gcd (with lust / meta well under 1.0 seconds, so gcd capped sadly). Each lava burst hit for ~510k + 100% overload chance at ~400k each. Easy 1 mil if echo proc'd, didnt look for echos tho.
Not sure what gear you are using to only get to 81% (might just be the gems, i will try int / mastery hybrids and i think i can still have 100% mastery). The gear i am using is
http://us.battle.net/wow/en/characte...steel/advanced with 5/5 new tier and 2 trinkets. I am still missing several mastery pieces as well, such as Loa mastery bracers, Ra-den belt, Iron Qon ring, etc.
Either combo of double amp or amp + cleave trinket puts me over 100% mastery. Double amp being the bigger damage increase becauses the crit damage bonuses stack.
EDIT:
These are my stats sitting in town on PTR, unbuffed (minus the 10% mastery buff ele always has on). This is with double amp, and INT is at 23,000. INT is a little low, because i only changed a few pure mastery gems to hybrid int/mastery gems. But, as you can see, haste is still just fine, mastery is capped, hit is capped, and this is with mostly 5.3 gear equip. Cant imagine we will be in a good place at all with full heroic TF, since we simply wont gain much damage from the gear, minus some INT upgrades because we will be capped on both haste and mastery very very quickly.
This also leads to Elemental Blast being unusable imo. PE is still very good, and havent tested Unleashed.