I imagine you would just have to run the numbers while considering things like, how long you want to work, how much the pension is worth if you ride it out, the income lost each year by not going to private practice, difference in benefits, access to retirement accounts, work environment, differences in the job like hours, environment, and production pressures.
If private practice would pay you a LOT more, and you could easily save enough to exceed the value of any pension in the amount of time you wish to continue working, then it seems easy. But if the PP job is brutal and burns you out too fast to work that long or has a small pay bump, then it doesn't seem worth it.