Been thinking about this topic, and here's my 2cents.....
More important than the capacity of the winch you choose, is the quality so you know it will work when you need it. Your training and knowledge of how to use the winch and accessories so that it can be completed successfully and safely. Having the proper accessories (first and foremost winch controller, gloves, shackles, snatch blocks, tree savers etc). Making sure to have a high quality line (whether synthetic or steel) and that it's not mired in a nest that can't be pulled out when needed. Lastly, use any other means you can in conjunction with your winch to give you an advantage in the pull (i.e. Stack rocks, power the drivetrain, etc).
Most situations should only necessitate a small assist from your winch. If it is really stressing the winch that much, step back and see if there are any other options because failure may be just around the corner. At the end of the day I'd rather have these factors and an 8k winch than 16.5k and missing any of these steps.