Would some of you more knowledgeable folks please tell me the main differances between the Zipp 440 and 404 wheelsets?? As I understand it, the 440s had foam cores whereas the 404s do not and are therefore 40 grams heavier per wheel. Since I am NOT a pro/high Cat level rider by ANY stretch of the imagination, would I be better off with the 440s for an occassional TT (PR type) or Biathlon?? I have seen that the 404s can be quite costly, even used on Ebay and the 440s are a little more reasonable. Thanks for the info!!