well fair enough that it might not make that much difference, but it's not exactly mild variation is it? iirc it was only about 5% off laing's figures at the time...6 vs 12lpm at 2 mH2O is not what i'd call a small difference. max head is not really that relevant, as stated. to match the 'old' version at 12lpm and 2 mH2O, the 'new' revision would have to drop to 1.2mH2O. that's quite a difference.
btw, i am just quoting numbers at you. as i said, w/c n00b, so clueless as to the practical effect of the above

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