88mm = .020" overbore. It will add a good chunk of cost and time to machine. It's not going to give you any gains that you'd notice. The big determiner for if you should get it overbore to 88mm is if your PWC without machine work is over .005". If it's over .005" you'll get some piston slap on cold start (it may even hang around once warmed up too) and the piston and cylinder walls will wear a lot faster. Overboring lets you control the PWC to be where you want.