Maybe I missed a change, maybe I misunderstood, or maybe the in-game stat reveal was broken at first - at any rate, I thought the Arena IX booby prize Succubus Kiss was +5 fire pierce only, but it is in fact +5 physical AND +5 fire pierce. The current thinking is that elemental pierce is as good as physical pierce in PvP, so SK is effectively +10 (mixed) pierce, i.e. +1% att. So with my 5300 effective att (eAtt), SK gives 53 bonus att on top of its intrinsic 9.7 eAtt - substantially preferable to Lava Inferno's eAtt of 48.3.

It is still not on par with Deaths Embrace nor even Whirlpool, but instead of the 13360 eAtt I originally calculated as necessary to make it overtake Deaths Embrace, I only need 6680 eAtt. If I keep putting on 8.4 eAtt per level then I'll be there in 164 levels, not ~960 levels as I originally figured. Whatever, it's better than my previous best-in-slot magic, Lava Inferno.