When ELITE? Seriously...
Having nearly 10k of total kills, it fells im stuck or something. Did get my Deadly rank, within 4500-4600 total kills, and its was during Lugh CG... And managed to hit above double of my kill count since, yet still Deadly. I do both RES and war zones to keep my counts on similar level. Usualy gained next rank when Doubled my totals, but it wont worked with final rank.
I think the SHIP you flying while killing it makes a noticable diffrence... And RES hunt is slower over war zones for sure. There is something beside "kill count" within rank gain. Some kind of "value" points, as Elite Anaconda sure has more worth of "something" over novice Siderwinder beside kill count. Kinda like XP but hidden.
Same thingy for us, If I kill that Elite Anaconda with stock Sidewinder, do I gain more points or same amout if kill that NPC with my 300M Anaconda? For me, seems it works kinda like that. Otherwise, we all would have rank up, by gain same kills amount... yet anyone seems have own unique "total" from stats (assa,bount,bonds), when they rank up.
Im not 100% sure about ships we fly atm, but im pretty sure about "vaule" of npc.