I really like my 6" Bandit, too. Having a lineup of guys wanting firewood, and a firewood saws that sizzle like there's no tomorrow really allows a commercial arborist to get away with the smaller size chipper.
I'm at a point where I've gotta be thinking about a new chipper. It's a tough decision. If I go bigger, I'll just fill up the box faster, make more trips to spill chips and all my firewood guys will get less firewood. I won't chip any faster, just a bit bigger. The Bandit, once I got all the modifications dialled in, has been beyond satisfactory. I wish I could say that about all my equipment.
If I was running a crew of guys I don't think the 6" would stand for it. It's more a 1-2 man machine. Get a couple guys trying to ram material down it that's too big, they'll either slow production or send the machine to an early death.
I fear hiring a guy who's used to feeding a 12" model. He'll naturally want to go big. A 6" will gobble brush all day long at 90 feet per minute, which is rippin, but you have to stay under 6" diameter. This would be totally foreign to a guy who's run bigger chippers.