Many different production types. Example: KTM Vertex is not the same piston as Vertex after-market type. Check weights! But both are quite good.  Some brand pistons are different heights, so your squish clearance can change.    VHM billet pistons do actually have a run in coating!     The 12 degree pistons change the port timing and also are flat , increasing the top end power .  Most manufacturers say to replace small size high rev pistons at 10 hours.  Most riders do them at 20-25 hours.     Using the dyno to test, most engines see more power made if a piston is replaced after  about 12 hours.   After about 12 hours some exhaust gas pass the compression rings, and enters the crankcases , this reduces the power of the engine a small ammount.   Using a new piston before an important race meeting is well worth while.  Modern hard coated cylinders with light alluminium pistons dont take long to run in at all.  Do not add more oil for run in.  Deglasing the cylinder when replacing the piston is worth doing, using only a soft scouring pad.  Adding a thin layer of oil or grease on your base gasket, will allow you to reuse it.  Cylinder head orings must be changed each year at least.   Always replace exhaust orings each piston change as well.  The KTM sx65 powervalve operates on exhaust pressure, its different, like the kart engines, so any change in the pressure-compression, changes the power curve of the engine. A new piston or even  Silencer repacking changes this too .  On the dyno, a new silencer fitted to a sx65 with reduce the power, for about 20 minutes!   Never fit a new silencer before a race to a sx65 !