Sunwell bosses are easier at 70 that naxx was at 60. Average time from encounter to kill a sunwell boss is 5 or so days. The time from an encounter to a kill for the horseman at 60 was 7 weeks. Naxx for 60's was MUCH harder than Sunwell for 70's.

first of all t6 isn't as good as its made out to be, with full t6 and whoring all the JC only stam gems on the PTR i only had about 15k health on tank, with non-set random epics i have 21466 health, and way more defense/dodge/block/parry than with t6, 2nd the 4 horseman are hard yes, but not if your other tanks know what they are doing