The right sized single could certainly come on earlier than twins because you have 6cyls driving one medium exhaust exhaust wheel. On twins you effectively cut the engine in half to drive two smallish to medium exhaust wheels, this is what drives the lag profile.
Also before you go and buy random parts talk to a workshop in person and give them the problem statement. This might save you a few $k in parts only to find it does nothing to shift the boost profile where you expect it, ie I think you expect a 600rpm+ shift in boost profile from those parts, I'm not convinced they would get anywhere near that amount of change in response.