Just my opinion, but I think the difference in true maneuverability is going to be negligible. Hopefully, you won't be contending with so much "traffic" when tubing that the 30 vs 45 will make a real difference. We have spent a decent amount of time tubing behind the 45 on Lake Washington and I have never wished I had better maneuverability.
Again, just my opinion, but I don't think you should buy based on a beginner vs advanced surf wake. The reality is that the better surf wake you have, the better you will be able to surf... regardless of how experienced you are. If you are going to be doing a lot of surfing, buy the boat with the best potential surf wake. I believe that is the X35 between the two you are considering.
BTW: since you are local to the Seattle area, talk to Darren the GM at the MC dealership in Issaquah. I know they have surfed behind the new X30 and can give you a true comparison. He's a good guy and will give you a very honest answer.