I can see how a 8-6 or a 6-2 evo or better has its advantages, but how often do you find people that do it? Is it only for the top players or people that sink alot of money into it? Its hard enough to get 4 hr let alone 6 or 8.
6-6 is what most people who know what they are doing aim for, as the post above said it's 99.5% efficient.
To get the last 0.5% requires an 8-14, or over twice the enhancement and two more cards. Most people will pay a lot more for a 6-6 in trade etc. IF you can prove it . but I don't see people calling foul very often on the couple hundred points maybe if a card wasn't an 8-card max.