Need some advice - XJ900 or FJ1200?

Hi all. Need a bit of advice. Am looking to get either an XJ900 or an FJ1200. I'm leaning toward the 900 as I prefer the shaft drive but depends on what comes along at the right price

Thing I am most concerned about is I have no idea what would be considered high mileage for either of these bikes. I'm pretty sure both engines are quite robust and will take quite a lot of punishment but, for instance would you say 50k is getting into problem territory for an XJ900?

Most of the bikes I am looking at of course are 15-25 years old and one would expect the miles to be fairly high but I just wonder if I buy a bike with 50k+ on the clock and given that it has been well maintained and I will maintain it just as well, how long before one would be looking at some serious engine work?

I know these are difficult questions to answer as there are a lot of variables involved but, as a general rule, are these bikes good for high mileages?

Cheers

Saul