Greater minds than mine have considered this topic. See this <a href="http://www.broadbandutopia.com/caandcaco.html">resource</a>. This <a href="http://discountcablesusa.com/ethernet-cables100.html">website</a> has the following statement: <b><i>If you're cabling a mission critical system or you want your network to be future proof, go for the CAT6 cables (and patch panels and connectors), but for the average home or small office network CAT5 or CAT5e will be just fine.</i></b>
From Carrie Higbie
Category 6 cabling provides better balance (less susceptible to noise) and since in most cases there is a bit more copper in the conductors, it may provide better heat performance than category 5e. For data centers, the TIA standard recommends category 6 as a minimum, although that standard published a full year before the 802.3an and limited distances for 10GBASE-T. It is important to note that for 10G, 6A is the minimum recommended in the ISO data center standard. The testing and mitigation needed for category 6 to run 10G are cost prohibitive to new installations. It is true that 5e will support gigabit, but that is only if the system has been properly installed and properly tested with a tester that has been recently calibrated and has the latest hardware and firmware and it passes all parameters. In fact, for 5e, it is suggested that all links be retested to assure they will run gigabit in an error free manner as there is so much 5e that has been improperly installed.
All that said, as new applications are developed, if you own your building and you plan to stay there, it is in your best interest to put in the highest performing cabling system available. This assures that current and future applications will work. Currently the highest performing cabling system is 7A/class FA.