Bisiclly...
Engine make the most power at 80 odd degrees (so i'm told)
The fuel temp will be direct result of a number of thing. restriction through the lines the actual heat of the day heating fuel in the tank and the fuel rail which is conected to the engine so is obviously gunna get hot...
I wouldn;t imagine that engine bay heat would have that much of an effect on fuel temp other than if it effected the coolling capabilities of the engine causing the engine to get hotter in turn transfering more heat into the rail...
Do to the topic of your original question...
Yes I beleive that if your carbon bonnet was a non vented item then i would result in an increase in underbonnet temps..
But most carbon bonnets are vented in some way.. and are usually done in a maner that any sort of wind flowing over them will suck air from under the bonnet.. Causing a heat reduction...
If your bonnet is a non vented style one and your concernd about heat, just space the rear of the bonnet up with a few nut/washers.. This works fairly well at removing hot air from the bay..
And flying monkeys DO exist... I seen em on TV..