I'll play devils advocate.......Don, I've found is that we'd rarely want to take our DT1 cylinder out that far. Because they're reliable old buggers most that I've seen haven't gone past second or third bore, 1mm would be tops. If you find one that is 1.5 or 2mm over and you need to replace a piston, there are plenty of replacement cylinders out there with plenty of bores left. It'd be nice to have the big bore option but I wonder how many folks are 1: building/riding/racing piston port DT1's and 2: how many of those that are, need a piston that big?............Just my 2c worth.