I found this while searching, because I remembered it but not much about it
"If you may recall, Killing Spree started if you or your group if you killed an initial mob quickly enough (although it was primarily designed to be a group mechanic, not as easy for solo players to initiate). Once started, you and your party would get a +5% bonus to killing XP and have a timer (~10 seconds or so) to kill another mob and go to the next stage of the killing spree, or else have the spree end entirely. You could eventually work your way up to stage 4 (+20% XP) within four mob kills."
Maybe that is still intact, but also intact for PVP which it was never intended for, also possible that there is no cap, also doesn't end after death, and unaffected by a timer.
I check SC score boards and look at the highest amount of xp and check their stats during the SC, but I can't really tie in to what gives the most bonus xp. One time the person with the highest killing blows with no deaths, then the next the person with lots of killing blows and lots of deaths.
Source
https://waaagh.wordpress.com/2008/10/03 ... y-knew-ye/