The zilla loves to breath! Long ago Arlen at LRD told me that in his dyno testing the vm44 mikuni put out 3hp more on the topend on a stock nonported fmf equipped zilla over a Keihin pwk39 with no hp loss on the bottom.  I'm sure with even more mods the difference becomes even greater, plus I love the look of the old school roundslide...gives more of the sleeper effect to the squids at the hill.