I'd go ahead and run an 84.5mm bore. If you're not too great at engine building and you're worried about rebuilds, you might want to go for 83mm, maybe 84mm. I would boost up to 85mm bore, and starting at 84mm gives you 2 rebuilds left in the sleeve- 83mm gives you 4 rebuilds. Don't increase your stroke unless you want to add on a deck plate. Sure, you could run higher pin pistons, but you generally want a good amount of material in the piston crown on a high power boosted application- and raised pin pistons tend to be thinner up top and have weaker ring lands.