I think the NO vote is worth the gamble. I doubt very much that management will pull the current offer if in the unlikely event actual RPI is worse. I would like to make an informed choice based on actual not predicted figures.
Like anotherthing said, it's not about purely economic numbers - the threat of industrial action is one that will make the airline sit up and listen .
The alternative is that a pissed of bunch of ATCOs ATCE ATSA etc will become highly demotivated and give up extraneous duties and not give that extra mile that we all give as a matter of professional pride and a few hundred thousand pounds' fines should cause managements ears to prick up. I for one am getting more and more pissed off with NATS management as time goes by. The pay is their final chance at redemption (in my opinion)