^ I don't think more cam would help you. Have you tested turbine drive pressure? I think with a single that size you would find it's getting up there and that's what's making it peak early.

You could keep your current cam and go to twins, reduce turbine drive pressure at the same boost level and pick up a ton of power and 1000 usable rpm.

More cubes would make less power with your current setup. (again because of drive pressure to boost)

The manifolds would have to be horrible to pick up anything with headers so not much gain for time invested if what you have fits well.

Agreed that an intercooler would gain power.