NASA developed a 4million horsepower engine with one VERY large turbo feeding into another large single turbo, then that feeds 2 x smaller twin turbos (all in sequence) and makes 400psi boost. They now use these engines in their planes that fly on the edge of the atmosphere or statosphere. The turbos are 4 times the size of the engine itself, which is no bigger than a 4 cyl engine....
Also, I can't remember who, someone on here will, but a rally car driver had a Delta S4 which was supercharged and turbocharged. Best of both worlds....
My 25 to 30cents worth