Remove the 12.5% gem, you go from .6036 to 1-((1-.6036)/.875)=1-(.3964/.875)=1-.4530=.5470. In other words, when you remove a 12.5% gem that I assume you have from your hat, you drop to 54.7%. Now reapply the 25% gem if you get a max rolled Leorics--> 1-(1-.5470)*.75 =.1-(.4530*.75) =1-.33975=.66025. Therefore, if you got a Leoric's and were sitting at 60.35% before, you would go to 66.03%, approximately. If you did NOT have a 12.5% gem before, Autocthon's math is good, you would end up right at 70%.
Soft (gear) cap on live is ~73% for non monks, ~75% for monks. When taking the new Leoric's and the new Vigilante belt into account, that may come close to 80% for all players (monks only had an advantage due to a spirit stone that could roll CDR).
Hard cap (with buffs from Empowered Shrines and Channeling Pylons) is 89.99%. As an aside, you can hit that with an Empowered Shrine once you hit about 65% CDR without it.
Crap I forgot the maxxed out IAS/CDR gem, which would be another 20%...with max stats on that, you could shave off another 2.15%, which would put you to 80.67. In other words, yes, 80% CDR will be achievable theoretically; that means permanent Serenity for monks, and permanent Archon for Wizards (those are the two classes I play; not sure if 80% is a magic number for any other classes).
Will it Cap out at 70%(or is there a cap on CDT) or will it go to 85.35%?
Assuming you had a diamond in your helm already your new CDR is 64.6 if my math is correct. (12.5% in Helm -> 25% in helm)
If you had no gem in helm you reach 70%.
Soft (gear) cap on live is ~73% for non monks, ~75% for monks. When taking the new Leoric's and the new Vigilante belt into account, that may come close to 80% for all players (monks only had an advantage due to a spirit stone that could roll CDR).
Hard cap (with buffs from Empowered Shrines and Channeling Pylons) is 89.99%. As an aside, you can hit that with an Empowered Shrine once you hit about 65% CDR without it.
**EDIT**
Passive--.8 Paragon--.9 Head--.75 Amulet--.92 Shoulders--.92 Gloves--.92 Belt--.92 Ring1--.92 Ring2--.92 MH--.9 OH--.9 Borns--.9 Cap Crim--.9
1-(.8*.9*.75*.92^6*.9^4)=1-(.2148)=.7852
So new theoretical max CDR is 78.52%.
Close enough anyway