It depend on your stat and characteristic of your pokemon (Nature/IV/EV). Also no buffed to E4, it still keep the same things since my post.
UPDATE: Just beat E4 with team below (gengar was lvl 91 though) and only used 5 revives, 2 hyper potions and 2 full restores. Thanks so much for this guide!
Okay I'm working on EV training, will report back :D
This is what I have atm: