How long can you drive on synthetic oil?

I am using full synthetic oil in my car and I know it says it runs 5k miles but I was wondering how much further it can run? How long can you drive on synthetic oil?
I have used Amsoil in several vehicles over the years, and I change oil once per year, or 25,000 miles, as they suggest. I have never had an engine failure of any kind. Plus, winters are cold here, and my cars are never garaged. The first winter I used Amsoil, I noticed that the engine cranked as easily at 10 degrees below zero (Fahrenheit) as it does at over 100 degrees above. That convinced me that it is a better lubricant, and I am still convinced.How long can you drive on synthetic oil?
4 cyl.- only 5000 miles


6 cyl.- 6000 miles


8 cyl. 8000 miles





Add 2000 miles if you run a K%26amp;N oil filter