This is an excellent article about installing Cat5e, vs Cat 6 or Cat6a. Here's a excerpt, but the article gets into much more detail as to why:
"...people who are paying extra for Cat 6 and 6a assemblies, and who think that they are paying that little extra for the sake of "future proofing," not only are not getting the future-proofing they're paying for but are in many cases getting cables so bad that they may be choking the customer's existing Cat 5e network."
http://www.audioholics.com/audio-video-cables/bjc-cat-network-cable-quality-interview
"...people who are paying extra for Cat 6 and 6a assemblies, and who think that they are paying that little extra for the sake of "future proofing," not only are not getting the future-proofing they're paying for but are in many cases getting cables so bad that they may be choking the customer's existing Cat 5e network."
http://www.audioholics.com/audio-video-cables/bjc-cat-network-cable-quality-interview