I think that the best camping spot of Heart of Ice is King room. I oftenly found the goblin wizard on center of this room. Fortunately, it can be found easily. It looks like COMMON drop.
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But Heart of Fire was not common for me. I think that Inferno Goblin Wizards don't have static spawn point. Maybe their spawn points can be random. Also they dropped Heart of Fire uncommon or rare.
I camped Bartender room for Heart of Fire when I was level 31 with my friends. I believed that I must camp at Bartender room for Inferno Goblin Wizards. But I found that in Kindle room and lord room recently.
BTW, Staff of Temperate Flux is the valuable item from the Temple of Solusek Ro, though it's not so easy to get.
And you can solve this quest as multi-quest. Good luck.