FormuIa said..
I've been riding a carbon race 95 mast (original) and a custom mast (measured to be even stiffer than C600). Going to a stiffer mast is a pleasant experience which transforms in a more stable and faster ride. Going back to a more flexible mast, especially torsionally, is quite a disappointment.
Therefore, maybe avoid trying out the C600 if you won't buy it :) It does make a difference, but then again, even the IQ mast is pretty stiff torsionally, so it's a good middle ground. And if you don't try either of those two, you'll be probably be happy with C300 (or original 95) too, as long as you don't race or ride in demanding conditions (20+ kt, chop/waves).
And that's my problem, I have original STB carbon Race 95 mast which seemed fantastic borrowed an iQ and thought wow so was thinking is the C600 a double wow. We sail in some pretty aggressive chop, tide and the full wind range whilst using a selection of front wings and fuselages.
Thanks for your comments