Warm weather fabric questions

From what I've read, certain weaves such as fresco and fibers such as mohair breathe better than pure worsted wool and are better suited for warmer weather. I think that worsteds generally have to be in the 8oz/230g to 9oz/260g range to be considered tropical weight. For fresco weave or mohair blend fabrics, do I need weights that low to remain cool? Of that fabrics that I've seen in certain collections, most frescos don't go below 11.3oz/320g weights and most mohairs don't go below 10.5oz/300g weights. I've even seen mohair blends as heavy as 15oz/420g which leads me to believe that those blends are either much cooler than pure worsted or some people like mohair enough to want it for winter suits. Any pointers would be appreciated.

Thanks,

dan