My bike is at 88 mm, which was done when Millennium Technologies re-sleeved my cylinder. They put in a LA sleeve and then bored it to 88 mm to fit the Wossner piston I already had. I purchased my running 1988 engine off eBay, and it came with a cylinder that was sleeved with a 1989 and up sleeve and had no KIPS valves at all. I purchased another head with KIPS valves and it was already sleeved and bored to 88 mm, but it was worn out. I only rode the stock bore 1988/1989 sleeve head a little bit before redoing he engine, and I don't remember a ton of difference in vibration between the stock bore head and the 88 mm head. My bottom end was done when I bought the motor off eBay, and it looks to be welded and balanced, so I may not be the best person to comment on vibration. When the carb is set up correctly, it really rips.