R2D- how far is the ruck run again? I agree with what you said about blowing up, it's not a 100 so even a blow up shouldn't be too bad. Hell, if you think you have the fitness to challenge the CR but it's close then a blow up shouldn't even be bat bad of a blow up. Just be damn sure you're being honest with yourself in your fitness. If the weather spikes then I'd give up on the CR (don't pull a Jim at WS) and just run for the win.