As an aside, depending upon the situation, if a runner is going and the pitch is in the dirt the catcher may attempt to pick it rather then block it. i.e. the base is stolen whether its blocked or goes to the backstop so attempting a pick and throw is a viable option.
Personally I feel 80 is a very workable speed for catchers at the D1 college level.
I read a lot of discussion on arm speed, blocking, framing etc..,, in many ways its all meaningless if the player can't hit college pitching. A catcher throwing 90 who can't hit can be made into a pitcher, so he is a low risk from a recruiting point of view, a catcher throwing 75 is a high risk recruit if the bat is in question because there is nowhere else to play him.