Depends on what I'm doin. If I'm climbing doing trims, might not go through a full tank on the 200. Even a big takedown rarely go through a whole gallon. When we were cleaning up after the fire, though, I might run 2 gallons through the 660. I had a great groundie setting ropes and pullies for what I couldn't wedge, and I might run through a whole tank without ever shutting the saw off.
As far as hours, I'm at the point where I don't like to climb more than 5 or 6 hrs, and even an 8 hr day on the ground wears me out pretty good. You burn. 2 gallons through a 660 in a day and you feel it the next morning for sure. We had a job clearing dead pines down a half mile drive and my groundie offered to carry the saw back for me, and he was moaning by the time we got back to the truck, it was kind of funny.
Hey cedar, just a heads up. We went to pick up some cedar planks in Lampasas last week, and they were out of mesquite. He said all the mesquite cutters he had went to the oilfields. If you've got a decent source out there I can hook you up with him. Jeff