I'd take over 6 simply because the number seems low, more than opinion. We'll probably be pegged closer to 7.
Those over/unders from 5 Dimes linked earlier in the thread were very generous on the over. I'm skeptical they were actually bettable at those prices. Not only were the numbers high but the juice was tilted severely to the over more often than not. For example, the Dolphin price was quoted at 8.5 over -195. That is roughly the equivalent of 9.5 flat, since you are asked to wager 195 to win 100 on over 8.5.
Every team could have been wagered toward the under and you'd need a weird split to lose, based on those prices. Houston was absent, which was strange. But disregarding Houston the number of wins added up to well over 256, which is the league split among 32 teams. Normally the sportsbooks do shade toward the over since the public prefers to play overs, but not to the extreme 5 Dimes used.
I checked their website and the numbers are there -- and the same as indicated in the February link -- but the prices are down. In other words, not bettable. They may have been briefly bettable until the wise guys slammed the unders and the prices were taken off the board.
Check the Props box under Football at this link:
http://www.5dimes.eu/livelines/livelines.aspx
The college over/unders are playable but not the pro numbers.
Sportsbooks these days are very conservative on pro over/unders in every sport, putting them up much later than a decade or two ago. Too much volatility, based on late acquisitions. In the NFL it's rare to see anything prior to the draft. Normally they begin popping up within a few weeks following the draft.
This is a longshot but perhaps 5 Dimes had a rogue employee who put up intentionally bad prices, allowing friends to take a pop at them because he was promised a kickback. Sounds fanciful but I've seen that a few times in Las Vegas, most recently at the (now extinct) Frontier about 7 years ago.