Find a used bike. Plan on installing the 685 kit.
For 20 years, KLR650's were produced WITHOUT systemic excessive oil consumption problems; this with engines displacing nominally 650 cc.
Thus, I do not think latter-day oil consumption problems are a result of KLR650's NOT displacing 685 cc.
While the Schnitz kit may not be plagued with excessive oil consumption problems, the cure lies somewhere besides the displacment increase. For example, maybe the ring design/construction offers lower oil consumption in service.
Kinda hard to explain, I'll take a stab at an analog, or parable: Once, long ago, a pig was trapped in a burning house. After the fire burned out, people went in to inspect the damage; one visitor touched the carcass of the pig.
The pig's body was still hot from the fire, burning the individual's fingers; he put his fingers into his mouth to quench the heat . . . mankind, for the first time in history, then tasted roast pork!
Finding the dish deliciious, the humans of the planet, whenever they had an appetite for roast pork, would tie up a pig in a house and set the dwelling on fire. After the conflagration, the people enjoyed a feast of roast pork.
Sometime later, more efficient means than burning down houses were developed for cooking pork.
My point: Going to a 685 kit to solve the oil-consumption problem on a KLR650 seems to me not unlike burning down a house to roast a pig. You'll come up with roast pork, but more efficient means may exist to produce that menu item.
Similarly, I would hope oil consumption problems might be solved with KLR650's by means other than going to the extent of installing a big-bore kit.
What means? Re-hone? Re-ring? I don't know, but--I have a hard time getting my mind around the notion that one, and only one, cure for excessive oil consumption on a KLR650 is installing an aftermarket big-bore kit.
How would one explain the 20-years of non-oil glutton production?
For an update, other than a window of '08 KLR650 production, has excessive oil consumption continued to plague KLR650 motorcycles?
If the problem is a result of faulty design, materials, or workmanship, I'd hope Kawasaki does the right thing and warranty-repairs the afflicted machines.
Disclaimer: The parable isn't original, see "A Dissertation Upon Roast Pig:"