I'd vote for a 6" SS blade.

This length gives us the option for sawteeth (or ST/no teeth grind) for the knife.

I'd prefer serrations to sawteeth, but I know that RMK does not offer a serrated edge. I have a SOG Scuba/Demo knife which has wicked sharp top edge serrations. They're perfect for a dive knife, and would, in my mind, be preferable to sawteeth for a fighter version of the Model 5.