hello the windleys!
My wife and I are about to leave Cairo heading south. So are likely to encounter the peak heat.
We can tell you what its like once we're the other side of the sahara if you'd like.
I think leaving it until September is probably a good idea, but it will still be pretty hot. We're hoping it will be bearable, but will have to wait and see. We've lived in Cairo for the last 3 years, and it's hasn't been as bad as we feared (especially given my scottish blood!).
Would be interested to hear from others about their views.