I thought a lot of things were very unlikely myself. And then I tested them.

Each manifold has a 1 7/8 outlet? Well you could test drive pressure at the manifold before the outlet and then right before the turbine. If there's higher pressure pre-outlet it could be a restriction but I doubt it.

T6 twin scroll narrows down to smaller than that not too far past the inlet flange.

Anyway as far as cam specs and RPM, I ran a 236/236 112.5lsa hydraulic roller cam in a twin turbo 427 LS7 and it peaked at 6900, barely dropped off by 7800 and made 1,341 to the wheels at 23psi boost.

Twin T3 PT67/66

Just saying that you don't need a ton of cam to make high rpm power with a turbo engine. If yours is falling off at 6200 I would start testing things as I don't think a cam swap will help you. JMO