As a massive battle is being waged on the the planet of Sanghelios, The master chief intercepts Darth Vader while he attempts to report to the Prophet of Truth. With both armed with lightsabers, a massive battle will insue.
Give Chief a psi blade and Vader his saber. I think that's what you meant.
Since the blade cuts threw a shield in one swing (in most cases..), we can assume Vaders blade would do the same.
Vader pwns the shit out of Chief with the force. However, Master Chief is really damn strong and Vader may have difficulty dodging automatic fire from the standard issue rifle.
I would love to see this animated out, though. That'd be neat.