Well the example I gave was pretty basic if a 3 inch exhaust was used for these 450wkw power levels obviously it would be too small but if an external gate was used it wouldn't be so much of a problem in this case it would affect the midrange dramatically from too much back pressure, think about it.My point was if you don't need to plumb the gate back in then I don't think you should but if your like Paul and you hate the sound of a gate then do it properly like he is and go big and all should be fine.
Anytime you merge two pipes into a collector there's always a compromise in out right flow it may not be much but it still exist.