I did email them twice (as I posted). Did you specifically request they clarify the exact situation as I did? Thats why I got a second reply.
Well, lets put this to bed shall we! I suspect the debate will continue far longer than either of us care to worry about it - not just on this forum, but also elsewhere judging by how much discussion there is on the subject!
What we can take from this Marc is that the situation is unclear. I was very sure of my position (and still am obviously!), but your email from Garrett, although similar to mine, implies there is no difference in response. I apologise for being so strong-willed with my opinion.

What we can deduce from this is that it seems even those who should know the answer don't.
Unfortunately, we're still no clearer ourselves! Perhaps the way to settle this is to test it back-to-back on a dyno somehow. We should be able to perform a series of tests with a dump valve whilst logging data and see the results, then overlay the data from running without the dump valve. I would guess that's the only real way now!
Did you fancy organising something? I'll be next on the dyno on the 6th September. I can do some runs then if you'd like? You're welcome to come along. Or if you're on the dyno before then. I can come to you? Should make for an interesting time
Thanks for such a good debate Marc - it's still not settled, but at least we're clear that there IS no clear answer!