I run 650b on my prophet.in the slacker shock setting the rear tyre will buzz the seat tube on full travel so I run it in the xc setting and have used some offset bushings.i have a 650 b specific fork and the bike rides fine.the bottom bracket is obviously higher because of the larger wheels but I can say I’ve noticed it.you can always run a shorter shock in the fr setting if you want to drop the bb height.cant bring myself to get rid of it still a classic frame.