Durlag's is the gold standard (pun intended), probably because it was a late-game add-on and rewards tend to increase as you grow in levels in D&D. Now, for the earlier game treasure troves, I find the map south of High Hedge and the Light House map to turn a nice profit. Also, I find scripted groups of adventurers to be quite lucrative, such as the ambush to the north of the Nashkel Mine exit, at Gullykin, etc...
If you're willing to part with magical rings that give you extra spell slots, they sell for a ton. In the Friendly Arm Inn area there is a hidden container with a Ring of Wizardry, which is worth 9000 gold. The Ring of Holiness you get from Mulahey sells for 5000 gold, over five times the reward you get for completing the Nashkel Mines quest.
Yikes! That's incredible! Haven't experienced BG EE 2 yet... so I don't know what gold gains are like there...
the time i hit the end of SoA i think i am somewhere around 450 000 - 500 000, and then when ToB hits near the end i usually end up with 1.2-1.5 million
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my record is just over 700 000 the time i hit sarevok in the under city
the time i hit the end of SoA i think i am somewhere around 450 000 - 500 000, and then when ToB hits near the end i usually end up with 1.2-1.5 million