Instead of having Washington sub for McBrayer, I think it would be smarter to play Washington with McBrayer and Coffey as his wings. Washington is at his best when he is pushing the ball up the court, but I just don't have faith in Konate, Fitzgerald, and even Hurt to make plays in transition. Konate and Fitzgerald lack the hands, Hurt is still young and inexperienced.
Plus, Washington is still learning how to orchestrate the half court offense. That's why I think it is imperative for him to be on the floor with McBrayer and Coffey at all times. If Washington is driving and gets clogged in the lane, being able to throw it back to the top of the key for a reset is needed. That's easier when McBrayer and Coffey are on the floor.
Mason is better suited to run the second unit when the rest of the starters is getting rest. Mason is better at finding a shot at this point and I think better equipped, passing wise, to ensure that guys like Fitzgerald and Hurt get the looks they need.