I dunno I remember doing at least 8-10 quests in searing gorge, some of the collection quests are easier than kill quests - drop rate was good and dropped for all 5 guys from 1 mob. I did get at least 1 full level from searing gorge, maybe 1 1/2, can't remember. Hinterlands was definitely better but I liked searing gorge. Just make sure to do the quests inside the slag pit also as theres at least 3 quests in there that take a grand total of about 10 minutes to do. and net something like 12k xp each.