Perron got 6.
10 isn't that outlandish given the context of it being right after a goal with seconds remaining in a non-hockey play.
It would be a similar logic to players coming off the bench. Does a goon coming off the bench mean a fight is going to be more violent than a fight that takes place if that goon is already on the ice at the time it is initiated? No. But if they need to penalize it with a long suspension because otherwise there is too much incentive for goons to come off the bench and interject.
If they don't give him a significant suspension, then it teaches players that you can engage in a non-hockey play with intent to injure when the game is already over and best case scenario you take out the star of a rival team with very little consequence to yourself or your own team.
If this was a goon/repeat offender type, it would be a massive suspension. Reilly's only saving grace is that he is a good boy and he is not strong enough to hurt Greig. The floor is 6, which was Perron's suspension (which had a failed appeal fyi). It will likely be higher because of the timing and context of it happening when the game was basically over.