I actually ran and coached athletes on the course. Guys from my team finished in 2:25 (debut), 2:27 (debut), 2:28 (PR), 2:31 (PR), 2:36 (PR), 2:38, 2:39, 2:40 (PR, me).
To say it was not ideal is definitely spot on. Could one run well? Yes, absolutely... I think just about everyone on my team did. Could it have been a better temperature for running 26.2 miles? Yes, absolutely... I think everyone on my team would have benefited if temps were in the 50s. To say otherwise is just plain silly.
Malmo, I don't care what the weather service says, in the sun, exposed, on that main stretch between 18 and 26, it was HOT. Not 70. More like 80+ on the street and in the sun.
I stayed very well hydrated. Took a Gatorade and 2 waters at nearly every station. 1 water for my head, one to drink from. This made a HUGE difference and certainly made it bearable for me. I am light (under 140 at race time, and almost 5'10") and trained at lunch time all summer in NY... so was used to the heat. But I can see how bigger guys, or guys coming from cooler climates would have had trouble.
How much of a difference did the heat make? I have no idea. I would guess for me, personally, not a ton of difference. Maybe in IDEAL conditions it was 15-20 seconds a mile from 22 on. But then again, it could have been raining, and I would say the same thing about having wet shoes. It could have been windy, and I could complain about the stiff wind.
To get ideal conditions is rare. But to say yesterday was ideal, is certainly not the case. It was as good as to be expected. But that is because you can't expect 40-50, no wind slight wind cover, etc.