I bored my xs out to 770 cc and the viberation at high revs is really noticable but it pulls quite well, its a fucker to kick over. My friend has bored his out to 900cc, they will go to that on the stock liner, fuck knows what that feels like at 70mph....I have biult several xs650 bobbers, i wont ever take them out to 750cc again, its a bit quicker but much better as a 650, top speed is not much different and its a smoother ride..after all its only pulling one person, if you change your sprockets to keep the revs down you can pull 90, fuck me thats gotta be enough on a hardtail......................