I know there's an 'all the gear, all the time' approach whose advocates say wear protective armoured clothing no matter what and if you don't you're being irresponsible, but I wonder how many of them have actually ridden for any time in a really hot climate. I've known two people faint under those conditions, with one actually falling off the bike. This, I hasten to say, wasn't in the UK and it was a lot hotter than it is here today (both in deserts) but the principle needs consideration. Are you a primary or secondary safety sort of person I suppose.
So I tend to take a pragmatic view. Armoured to the hilt and then losing concentration (if not actually collapsing) vs staying alert and possibly suffering more if you do have an accident.