$6300 is a good price for a King Quad. There are no recalls associated with that year so you would be good to go. As far as the air filter, the problem is the engine sucks so much air that the paper filter they are using lets dirt in when ridden in dusty conditions. Over time, this can cause the rings to fail. This has happened to a lot of people. You can do a search here or on Nyroc's site and see for yourself. Suzuki has not really addressed the issue other than releasing a heavier duty filter but that has to be ordered through parts. I don't know about you but most everywhere I have ridden is dusty at one time or another. The other quads out there have no issues. Suzuki should have done something to correct the issue but they haven't. So the best thing is to just change out your filter for an aftermarket one from the get go. There are a couple to choose from such as Uni, Twin Air, and K&N. You can find many threads on them as well.

As for the Vinson, it is a nice machine, probably one of the best in it's class. But it does have a solid rear axle. I prefer the IRS of the King for the smoother ride. But that is just my preference. As you get older, you appreciate that since you can ride longer and not get as sore. But either machine would be a good choice.

And don't worry about the 700 being too much engine. Both machines weigh about the same so you might as well get the bigger machine. Sit on them both though and see what feels comfortable. One other note is the Vinson is also available as a 5 speed with auto clutch in addition to the belt drive.

On the Ozark, why did they say it would not be covered? If it is only 2 months old, you should still have 4 months of warranty left. Unless you abused it, there is no reason they should not warranty it. I'd try another dealer or call Suzuki direct if you get no satisfaction from the first one.