Cylinder taper is the deciding factor. Cylinders do not wear evenly from top to bottom. The maximum wear happens in the top 1 1/2 inches or so of a cylinder. I consider a .003" TAPER, not total cylinder wear, to be a maximum. With a good quality rigid hone (not a spring loaded glaze breaker) I am willing to straighten out the taper and put a knurl on the piston skirts to re-establish the proper clearance. A race engine with forged pistons that do not have an Invar anti-expansion strut that must have a lot more piston clearance than one with cast pistons, a .005" clearance makes it sound like there's a bunch of little guys with sledgehammers trying to get out. That's particularly true when the engine is cold.
Jerry
