Yep, definitely Olympus. 
Make sure to take it alone as the lv 8 biome, big areas of it will give you huge hotspots. The build in this post got me 600k diamonds; I think sacrificing a few high level biomes (Mount Doom, particularly) worked out well as on their own they’d be smaller hotspots and took up a good bit of space, but removing them allowed some of the lower level biomes to merge into high ones (have diamond hotspot under some Island Trees even, first time I’d seen gems under those!) -
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