I used to play on Icecrown a few months ago, and I've always had 40-80ping, it was completely fine. And recently I started playing more again, played on Lordaeron and Frostmourne and I constantly have high latency. It's lag spikes 200ms-1000. I'm from Bosnia, nothing about my router or internet provider changed, and I can play other games just fine with normal ping.
Same here on Icerown, it's more or less fine (60-80ms) until a boss fight starts - I instantly get so much lag it's as if I DC'd 1-3K ms.
Literally unplayable. IB4 it's not my internet.