I leveled from 293 to 300 using nothing but infernal hordes sigils. While the xp buff is live, the hordes are just as effective. It took me 12 wave 10 sigils to go from 293 → 294. I can clear t 100 fairly quickly but the xp was just getting to be too little. Hope this helps break up the grind!
P.S. just in case be sure to always stack:
- a potion (rare potions from Dark Citadel merchant give slightly more xp)
- x3 incense (tier I,II,and III altogether)(rare incense from Dark Citadel merchant give slightly more xp)
- an opal (materials or equipment are my preference)
- an xp well from a Nightmare dungeon