That, of course, begs the question about going from Mas 3 to Mas 5. Is that even a path?
If I go to Mas 4, at least it will be something my local Mitel Tech will be able to get support on (and he's with Mitel Corporate, not a dealer). If I go to 5, I can guarantee you that I will be the first one he's ever done. If I want someone to mess it up, I can do that myself.