This has turned into a pretty interesting discussion.
laketreefarm, I hear you on matching chains, but if they are all matched to the lesser quality, you are still in trouble.
One more thing to remember, even if you have good chains, the binders are at least as important.
As I said, I replace with all G-100, but still had some G-70 binders. I was hauling a 140G blade one day, came around a curve on a rural road, and when I crossed the small bridge, there was a pretty good dip at the bridge end. I was going about 45 or 50, and did not have time to slow when I saw the dip. When I went through, both binders holding the rear of the machine broke in two from the flex in the trailer.
I did not know it right away, but suspected something may be wrong. I was only a mile from the site, so I slowed down and went easy into the job. When I got out to look, those 2 chains were loose, and only a couple pieces remained of the binders.
The G-100 chains didn't even show any marring where the hooks were, no streched links or anything. It pays to use good chain.