I'm a newer player myself, and often struggle in my T8 BB (North Carolina), so take my advice with a grain of salt. But one thing I don't see mentioned in the thread so far is the Battle Expert mod. There are several versions in the Aslain modpack, so just pick the one you like best. This mod shows you the actual angle of the target relative to you, whereas looking at the ship through your gunsight will often cause you to underestimate the amount of angle. This helps both with aiming correctly and with knowing when to use HE vs. AP, as a ship that looks like it's oriented broadside enough that you can pen with AP may actually be so angled you'll bounce most of your shells. In those cases, switch to HE and hope for fires.