one aspect of it is a misalignment of the upper and lower cases of the oil routing....possibly also to do with the oil pump, routing away from the pressure chamber side.....other then that the typical boost in oil pressure and you're golden.
I was gonna have my cases done and wanted to know the same thing, after calling around I found out that the zx10's really don't need it like the gsxr's. so it would just be a waste of money. Now I was told to do the oil mod to the crankshaft (get oil hole chamfered and polished) and any local machine shop can do that about $75.00.
well the history of the 10's throwing #3 rod is quite more often then not.....mind you if a 200.00 oil mod service saves you a crank/rod and other associated damages, then that good money well spent............all depending on how hard this this is gonna be tortured.
i've been running the high pressure relieve valve for a few years now...i'm not really hard on it as some would be, but drag racing has extra duty, so far it has kept my motors alive for the way and style I ride.