Maybe I am naive about some things, but IMO the piston manufacturer should know something about his own product and how it is intended to be used.....
If a forged piston expands more than a cast one, then it should be manufactured sufficiently under sized to fit the bore it is intended for.
If the engine is a 3.000" bore then the piston should be made to work in a 3.000" hole. If the machinist can bore the hole correct then why can't the piston manufacturer make the piston to the correct size to run in a 3.000" bore, and run to 1300º on the dyno without seizing. Why should we play by their half a$$ engineering and "tweek" the bore to accomodate them? Don't they know what the bore size is they are designing to and the expansion cooefficient of their piston alloy? Why should we have to reengineer their work (or lack of...)
To give them some slack... they don't have control of the air/oil cooling which does affect the actual temperature of the piston. Only the engine builder does and maybe few people actually are qualified to do engine developement work. In the mean time you seize motors.
You might as well start making your own pistons...humm I might give it a try... :bigt