Most the time a tug off a rock stuck is not much work for a winch, but you get in to even a small mud hole and you will give your winch a work out. Snow stucks can also really work out your winch, the longer pulls in snow can really push your winch.
I have seen the Warn 8000 fail, where my Warn 9000 got the job done, but I have been told the warn 9000 is more then I need. The one time I was able to drive back to camp and others had to leave the jeep over night was more then worth the money to me.
I have watched a friends Ramsey (9500 I think) pull him and me out of lots of stucks.
I would never buy a mile marker, NEVER! Over heating will make the winch a large and heavy boat anchor!
If you are only going to buy the winch once, my advice is to spend the money the right way now.