I'd stick with the 10 hours if I were you. Specially if you are going to run it anywhere near the top of the powerband. I doubt if anyone ran that spec at Rouen if they did it wasn't for 24hrs
As for the EGT, think what it is you are measuring, that would be GAS not aluminium. The gas is much hotter than the metal as the charge coming in cools the pistons and the water cools the block/heads etc. Most merc "tuners" are very sensitive about their EGT values. And don't pee your pants when you lift of in a hurry and it spikes.