Kill one or kill five? Obviously, most will choose to kill one. This is exactly every voter's binary situation on Steem: either vote oneself or vote others. Due to Steem's skewed economic incentives for self voters (or vote sellers, traders, exchangers, etc which are all effectively the same thing to maximise SP accumulation), most will choose not too sacrifice too much and reserve more votes for themselves.
A best example given by you, I will say that I have a negligible SP but I also think to save it by not upvoting the comments and save it for myself and few people, but I have seen people here upvoting minnows even if thier SP is reduced a lot, they don't care about the reduction of SP they just support . This blog of yours is quite informative.