You won't ever crit for that much on a PvP geared tank. Considering they have around 50% damage reduction from resil, 50% more from armor, even if they get 10 stacks, you won't crit that high.
Also, your target have to be under Find Weaknesses to be effective.
Btw, my biggest crit in PvE with Ambush is 50k, considering that I was fully buffed (no tolvir) and I'm using a 391 dagger. No, you won't crit that high on a target of your level, don't count on it.