How much mastery to use a poison build?

[Kassanova 0]

Hey all, I apologize if this is common knowledge, but my rogue is one of my alts and I don't know as much about the class as I'd like. I used to play outlaw just fine, but I'm interested in a strong spec that isn't so RNG dependent. I'm a bit confused as to how much mastery is needed to pull off a poison build vs a bleed a build. The talent guide says to go for poisons if you have a mastery-heavy build. What constitutes a lot of mastery? My rogue is wearing ilvl 847 with 27.79% crit, 7.83% haste, 116.2% mastery, 3.6/1.8% versatility. That is based on recommendations from Ask Mr. Robot. I primarily run mythics and I would like recommendations on the best tier 1 and 6 talent suggestions. 

Armory link: http://us.battle.net/wow/en/character/darkspear/Cowboyslim/simple

 

Thanks in advance!

[Furty 51]

You will still want quite a bit of critical strike for combo point gen, even with the Mastery build. Would recommend waiting another 20 ilvls or so, at least, before thinking of making a switch. Agonizing Build is also very weak for Mythic+ as it doesn't deal damage with FoK spread as Deadly Poison does, so its not a good choice for gearing up.