We used 0.5 in summer but also used the 1.0 a lot. I found then 1.0 great as it was toweling inside and a litle warmer than cotton on it's own. We had an evaporative cooler in Amy's room but it did get warm. I suppose layering could work too.

We have moved into a house with evaporative cooling in the roof so we will probably use the 1.0 a lot because it will be cool and a constant temp in her room. We keep the heater on 18 degrees and she sleeps with a Snugglepie? grosuit a windcheater and a 2.5 tog grobag as she was getting cold.