Lone wolf speaks wisdom.
I think anyone that is serious about getting a chipper and considers a 6x12 (bc700, bandit65xp, carlton 1260), will eventually want to move up. I don't think getting one of the above is necessarily a bad choice, in fact I say go for it. The reason being as soon as you see how quickly clean up goes with a 6x12, you'll soon learn how much it is also holding you back.
I was in your shoes last fall, bought a bandit 65xp with worm knives, a rounded anvil, tired kohler 25hp with an improper governor setting. It still upped my production by a significant margin over cut and stomp. Thats you first massive advantage.
Spent all winter doing tree work and made good money. Did the usual maintenance, knives and anvil, along with two upgrades, reversing autofeed, and a vanguard 35hp.. those were a big step up and if it fits it will chip.
I mainly do pruning in the winter and long with a few removals and storm clean up. Our trees aren't that big in nova scotia. I've ripped many 12" logs in half and chipped them, it just takes longer. Also, the 6x12 still require you to cut the crotches of hardwoods or limb up spruce tops. A 9 or 12 should have a big enough opening and crush power to not require this.
Also consider your tow vehicle, I have a 4cyl tacoma, I can't haul anything much bigger. The calton 1290 is the biggest I could haul.
I have no aspirations of doing tree work beyond what I'm doing, but I find myself wanting a bandit 12xp! Buy the chipper you will grow into, not the one you will grow out of.
Having said that, go for it, learn to adjust it and maintain it. Charge extra, even though your processing your material faster, in fact find out what it would cost you to rent for the day, and add that to every job at a minimum.
Cheers