Dunmunro wrote: "VV had extra steam available, without forcing the boilers because some of the turbines were shut down. The boilers are always the weak links when forcing past safe limits is required."
you are obviously right, especially on a long run, and I have pointed out this circumstance myself.
However, it is a fact that Littorio's never run the extra-power trials that were planned and even included in the contractual acceptance tests.
The normal full power trials ("prove a tutta forza normale"), when the ships developed over 139.000 HP, were run with 5,47 kg of oil per square meter of burning surface in the boilers, while the contract was including an extra-power capability trial ("prove a tutta forza massima") at 160.000 HP with 6,4 kg of oil per square meter in the boilers. Reference: E.Bagnasco, "Littorio" class battleships 1937-1948), chapter 4 pag.120 in the Italian edition.
Nothing happened, during the whole lifetime of the Littorio's, that could support the idea that the projected extra-power of 160.000 HP was not actually achievable. Vittorio Veneto behavior at Gaudo, when the ship developed 120% of the max power on the starboard machines, just lets imagine even something more than the contractual 160.000 HP.