Which thermostat do I buy?

[jcatalanello]

I have a 99 70 Horse Evinrude four stroke, and it had a stuck thermostat. Standard for that year is 50c. But I guess the following years they used 60c, and I have heard that I should use a 60c as they had a issue running too cold. So, should I stick in a 60c, or stay with the 50c? I live in Montana, just in case water temp etc has any effect on that.