I travel to Asia a lot and in the 32 C (89.6 F) temperature, I can wear up to a max of 10.5 oz. Finnmeresco is probably one of the more open-weave fabrics and I can wear the 11/12 oz stuff without feeling like I walked out of a sauna. I prefer the heavier open-weave stuff as opposed to the lighter tropical fabrics that don't behave as well.
Always found that it was the construction that mattered -- I could wear a 1/4 lined 11 oz Lesser, but not a 10 oz fully lined coat. And I almost invariably only wear lighter shirtings because to do otherwise when I'm in Asia is suicide.
That said, I keep to air-conditioned areas 99% of the time when over in that continent.