the best for removing a hole in wood is not a hole saw, its actually a forstner bit,
if you have to use a hole saw, drill as far as you can, then use a small drill bit and drill lots of little holes inside the circle, as many as you can, then chisel them out. but this is a horribly messy and crap way of doing it. just use the correct tool to start with which would be a forstner bit.
for those not sure what one is
although not what i normally use, this should do holes at 65mm diameter http://www.ebay.co.u...5-/320894847713