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@Dammit
Depends very much on where you put it - if you (say on a turbo charged car) put the valve pre-cat/post down-pipe then it’s going to be loud, and you’re rolling the dice on whether it’s nice loud or awful. But - most power.
My estate has four cats, two per side, and two sets of silencers - a valve that bypasses a cat/silencer per side would lift the volume a lot but likely leave the same tone.
Or you could put the cut-out post cat but pre-silencer (the Porsche Cup cars ran with just cats) which is emission friendly but still very noisy.
Turbo cars can sound quite good just with a high-flow cat, as the turbo itself takes a lot of noise energy out of the exhaust gas.