I have done up to T5 so far without real issues. I have mostly the weathered gear (head, chest, leg, ring, the rest being myth gear) and also have the atma bow (2 book upgrades for accuracy and 1 book for skill speed)
Rule of thumb from what i have heard from various people is to shoot for 500 acc on all classes, probably for T6 and above, EX Primals are not really an issue