if you race and think its going to make a difference in you getting on the podium you are living in a dream world.
Well, if your talking about putting an A/X lightness seatpost and a THM crankset on your bike that may be another thing. If you talking about the difference between a 105 bike with cheap tubular wheels vs. a Red bike with a set of Zipp 303's I'm going to strongly disagree. I too race 30+ CX races per year, and I feel every lap. Lifting a bike that weighs 5 lbs less over multiple sets of barriers and through slop makes a huge difference. 50 minutes in I can feel e-v-e-r-y gram, and I'm sure any elite racer would agree.
I don't think 5 pounds is going to put you on or keep you off the Podium. You either have the skills and power or not. Inside 2.5 or 3 pounds, your not going to tell much of a difference in the bike weight when racing at full speed. If a person wants to go WW on a CX bike and they have the money to buy replacements, I would say pick wheels. I ride light carbon wheels but I have 5-6 set glued and ready to go when I break a pair.