3cm isn't a huge amount, its about the same mount back as recommended on an AR6 (-2.5). But in my opinion that does make a difference. Moving 3cm back means you shit the balance point of the ski by 6cm, you have 6cm more ski in front of boot centre than behind. The wednesday has a wider nose than tail by a centimeter too, so that will add to the balance difference.
Its a tradeoff, I think you will notice the difference on rails but it wont be huge. If it is a pure park ski then its probably worth it. If its a mix of park/groomers and has to last you a long time, then it probably isn't.