I work for a major new heavy equipment dealer in the PM department. Our reccomendations when trying to expend OCI is to do an UOA with NEW unused oil, that way you get a base line, then do a UOA when changing the oil @ normal interval, then extend the OCI by 1K and see what the UOA says, then extend another 1K and se what that UOA says, ETC, until you get to the mark you want, 10K. It does take time, but that way you KNOW what is happening in your engine.
BTW, I UOA all my personal vehicles as it can prevent a major failure by trending the wear elements. Here we charge $10 per sample, a worthwhile invenstment, IMO.