Yes - the standard seems to me to be best set at the reasonable impression of imminent bodily harm or death. Then again, I don't think one should be expected to permit one's self to be put into a headlock or other disabling position. My guess, however, is that (in the US) people tend to consider a head-on charge from a crazed but unarmed attacker a more marginal case for armed peronal defense than a rape attempt (which I actually think most would agree is cause for armed self-defense).