My stock chain snapped on me about 5 yrs ago with 12K miles. I don't think it was user error. I'm pretty good with maintenance and keeping it lubed and adjusted properly. But for a replacement I went with the following. I stayed with the stock 530 size. I don't know if you remember Flood from CF, but he had a heavily worked over TLR and put a 520 on there and the chain let loose and took the block out with it, IIRC. G-rex can probably remember what happened better than I.
Here is the stock chain, it got caught in the bolts that hold the sprocket to the cush, and wedging itself in the swingarm, bringing the rear tire to a stop at 50 mph.
