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.
OK, I am thinking of a new summer suit. I have much experience with Minnis Fresco, was thinking of the lightest weight. But I have heard good things about some new H&S called "Cool Breeze" which is supposed to be about one ounce lighter.
What about trying the new Piuma (lightweight Brisa) from LL?
He just finalized the orders, but may be able to squeeze you in on the Navy.