I have been considering getting a 16GB card for my cenrto but I am trying to justify the cost differences. I can get a polaroid class 2 for $28 after rebate, a class 4 for around $50, or a class 6 for around $70-80. Does the centro even notice the difference and if so is there a cut off of performance gain? For example would itregister the difference between a class2 and class4, but would a class6 only act as fast as a class4?