The 8. 3L C-series engines weigh about 300# more than a 6BT...
They're a few inches longer and a few inches wider as well...
In all honesty, we're making a BOATLOAD of power with the 6BT's, and they're living through pretty much everything we can throw at 'em. I see no real reason to go with a 6CT - other than to do something different for a change...
Matt