The heat IS bad but bearable! I mean you gotta take it into account really, expecially if you want to freedive 1-2 sessions a day. Last year i was there in July and it was really great (minus the millions of tourists dumped by tour buses at the Blue Hole!) but I, for one, had to drink 3-4 l of water everyday, with some energy powders that you can find at any drug store in town. They come in 10 packs in a box, cost like 50 cents a box and are really great to replanish all what you sweat out, one way or another!
On travel from Cairo to Dahab, we (two of us) took a minibus, pick up from the airport and drop off in front of the BishBishi, our choice of accommodation in Dahab - great! it will set you off by 100 EUR (90 EUR if you know to strike a bargain - 150 if you dont

) for the whole minibus and about 6-7 hours drive. it's a great way to see Sinai too and have flexibility. Even in two, the price is acceptable (really depands on your budget though) but if you are a part of 3-4, it's a bargain and likely as fast as by plane (to sharm)+transfer to dahab!
serge