Mike - a lot depends on the quality of the previous owners (!). My '73 850 was rebuilt at 23,000 miles and was pretty tired even though I knew most if its history since new. The big end shells were showing wear, the valve guides & rings were all replaced and of course the Amal MK1's were scrap.....although it was not rebored. What it did show was that in my 20 years of ownership I remained unaware that a cam follower had let go in the crankcases at some point before I owned it and taken chunks out of one of the rods and pistons. So, if you've had it rebuilt it will be good for a significant mileage, if you haven't then a total strip is good for piece of mind....I think the 750 is sweeter and less stressed than the 850.