Use two turbos. If you're worried about lag or something run one big one and one small one. The small one will build boost while the bigger one is spooling up.
I have no experience with boosted engines. However I was a locomotive engineer and the END locomotives were blown and turbo'd 2 stroke. Pulled like banshees. The GEs were turbo 4 stroke and didn't pull as hard down low.
Has a combination of turbo and supercharger been done on an automotive application?