Depends on if you're looking to run with your QB, or if you are just trying to avoid pressure.
I use a slow QB (60 something speed) in my Fla dynasty, and use slide protection very often to roll away from an overloaded side to get away from pressure and set up and throw. I never look to run with him simply because he is too slow. He couldnt make it to the LOS before the D-line caught up to him.