Well, T5/T6 are really hard, and you kinda need something else to be able to do something. I plan on get the Archon set, stacked with a lot of Arcane Dmg. Before that, I don't think that T5/T6 are viable. T6 Mobs have way too much HP and everything can hit like a truck.
For your gear, well, First thing is to change your Chest. Another thing that would improve a lot your DPS, is getting one Andariel's Visage with Cold Dmg+Atk Speed+Crit. If you are lucky you can get one from Kadala.
I still think that Arcane>Frozen Orb, with proper gear you can have some insane DPS as arcane. With frozen orb you are more limited, plus I hate when mobs are too close and the orb explosion doesn't hit them.
I kill most elite packs pretty easily in a single black hole, so ~2-4 seconds, +area damage is freaken amazing on frost orb explosions. i'm currently working on aughilds chest/bracers so i can have 3pc bonus with the ring. As for surviving, it gets kinda hairy with bloodseeker/leaper packs but if i get the jump on them with agood black hole they die really quick.
As for arcane builds, i'll probably look into that, t5 packs seem to take forever to die right now so i am lacking a heap of dps.
I'm not exactly rolling AS it's just appearing on my gear as i get it, i realise it's ruining my dps, especially on a frost orb build, just running a little low on souls to craft better stuff/reroll
I'm mostly using chantodos for the bonus right now until i find an azurewrath/shard of hate, already have a very good rare offhand in my bank, just waiting for it :<
Concerning set bonus I see it missing those which should come from the Ring of royal Grandeur like the "+20 % life".
Also an other thing to mention, source seams to be bugged on armory, the range in damage are not those that display in game but dps seams to match the in game.
For the t4 farming I Absolutely second what MrWinklesaid I really doubt you are doing t4 comfortably even with 4 players in game. Currently with my gear I do t3 comfortably when I play alone but even in group I still think it is a bit slow on elites. So going to t5 and t6 will require a lot more dps to be worthwhile.