I've been playing with task-mgr on a second monitor. OOM at around 1.5gb on the current version, give or take. Don't recall prior versions exactly .
That's on XP, sp3, 3gb ram, 32-bit, Playing largest size maps, with ridiculous difficulty, with FOW off, in cloth-map-only mode. Loading a save in my current camplaign would start at about 1.4 ~ 1.3 gb, and I would die in less than 10 turns.
But turning FOW on reduces memory footprint by about 45%. Since doing that, haven't gotten over 1gb, and haven't crashed.