For me that seems quite important because, it seems to me that, corrosion is going to degrade the edge quicker. In a survival situation, I want to be sharpening as little as possible.
For an extended survival situation, I would choose INFI for the best corrosion resistance over SR-101 or SR-77. While technically INFI is not stainless, it is pretty close. I have an INFI knife that was in a car for years and when I finally looked at it, there was no rust on the edge, and I had not put oil or anything else on the edge as a rust preventative. Years ago I bought a Steel Heart II that had been seriously neglected, and there were only very minor rust spots - nothing that did not easily clean off. So do not worry about INFI rusting - with even occasional use, the edge will not rust significantly (exposure to salt water would be an exception).
Regarding the coatings, both the old smooth coat and the newer crinkle coat have proven to be very durable. It takes a lot of hard use to finally wear thru to the metal, and with INFI even if you do wear off the coating, it does not matter because it will not rust easily. As you alluded to, the edge is really the only place that rust matters on a survival knife, and with some use it is not a concern with INFI.
Based on your criteria of a 6.5" blade, I would recommend looking for a Basic 7, although it does not have an exposed tang. A Steel Heart II would be an excellent choice, but they can be pricey these days. Maybe a Tank Buster would meet your needs. Also look at the ASH-1 - it is available in .188", .22" & .32" blade thicknesses, both coated and uncoated.
Regarding buying knives on BladeForums, I have bought many knives from members here and the vast majority of the transactions have been flawless. There were a couple where the knife's condition was not quite as good as advertised, but that has been rare (and would not matter for a survival knife). Roughly 90% of my Busses were purchased from people on BladeForums.
Gene