How would testing hate gain be hard, even without resetting hate? Go get hit by grudge, hp, go back, kill some tonberries (keep track of how many you kill) and then get hit by grudge again. Calculate the difference in damage per kill. I don't remember if it is affected by shell / mdt / mdb gear, so it'd be best to not use that.

Or, for less dying, have a pet get hit by grudge instead of you.