I have been testing out MS recently and until I saw this post I thought it would be the best. I had no idea it would only proc once instead of twice.
With this being the case, fully stacking MS will give you a 27% chance to hit for ~35%+20% from survivalist =~55% of damage. If you were to calculate the average damage increase from MS, you would get .27*.55 = .1485 or 14.85% of damage increase.
At first I was calculating it with two chances, making it a 29.7% increase in damage which would easily beat versatility. With it only having a 14.85% damage increase in PvP, comparing it to versatility, versatility would be better due to the damage reduction and the stability of damage.
Hope that helps.