Some people posting on this thread think that because a chain is twice as long it should last twice as long. Don't forget, all of the chain moves at the same time no matter how long it is. It is true that any individual link on a short chain will bend twice as often while engaged with the cassette, derailleur, and chain ring cogs but a long chain seems to bounce more and that also causes bending albeit not as severe as around the cogged parts. Wear also has a lot to do with a person's cadence. The faster you pedal, the more often a chin link will engage a cog.

When my chain wears (stretches) I notice that it doesn't shift as smoothly. I have a fast cadence and used to get 2500 to 3000 miles before it was time to change the chain and cassette. At the time, I was oiling the chain often with those expensive wax lubricants you get at your bike shops. A few years ago I brought my bike into a bike shop with about 2500 miles on the chain and was told that the chain was marginal and will have to be changed soon. Then, instead of changing the chain I switched lubricants. I started to use chainsaw bar oil. I bought a gallon of the stuff for $15 US a few years ago and still had a lot left. 3000 miles later the bike shop told me that the chain was marginal. It almost stopped wearing. At the time, a lot of other parts were worn like the derailleur and the shifter and I was about to go on a long ride so I had the entire drive train replaced. That was well over 5000 miles ago and the chain is still good.

There are downsides to using chainsaw bar oil. It is sticky so dirt builds up sooner than with the other lubes while on dirt trails and it leaves a grease stain on the side of my ankle every time I ride. After a while though, the grease stain is not as bad and then I know its time to lubricate again. For less money, that lube works better than the expensive stuff. I do use a more soap now to clean my right ankle but soap is cheaper than the wax lubes. Pumice works the best of the soaps that I have tried.