if you're looking for more than 300 whp, its a good idea to sleeve.
some have run 400+ on the stock sleeves.... but it becomes more a matter of WHEN instead of WILL or IF.
piston bore depends on block bore.
81mm is stock
81.5 is "standard" overbore
82+, you're going to have to sleeve anyway.
so, ultimately, it depends on your goal, and more so, your wallet.