I'm sorry, guys, my bad. It's not an Mk5, it's an Mk2. Brandnew. I apologize for the confusion. From a physical point of view, I can't imagine a reg being good for 40% O2 but not 50%. Here is why:
With 40%, the pO2 at 3,000 PSI = 1,200
With 50%, the pO2 at 3,000 PSI = 1,500
If I dive 40% in a...