I've got four. Each time I roll some stats I'm somewhat happy with, I start again on a different Demise. I've only levelled two of them to 300, but I'll soon have the others up and ready for comparison. Perfect Balance doesn't seem to be in the roll list. After 21 attempts I've not yet seen it. Fitted Stock is essentially the same perk, only not as effective. Without Fitted Stock or Perfect Balance, you'll want to reroll. As the Stability is important for both PvP and PvE; if you want consistent precision hits at maximum fire rate. Then there are some up in the air stats, such as Firefly and Crowd Control, which are great for PvE, but pointless in PvP. Zen Movement however is effective in both. TLDR; If you don't get Zen Movement and Fitted Stock, you should reroll. The last perk is for flavour, but take whatever you get. The chances of rolling three of the perks you want is somewhere along the lines of 200/1