Derech HaMelech has it correct according to Rav Moshe Feinstein, ZT”L. But not necessarily “out loud”, just those things which need a Minyan should be said Sephard.
I saw R’ Moshe zt”l about a month ago, and I seem to remember that he says that all the things that require a Minyan should be said Sefard, but he also says that Psukei Dzimra (which does not require a minyan) should be said in the nussach of the shul, and only if one would get mixed up should one change to his own nusach, and in that case one should be careful not to say it loud.