It would be great for anything over 5 days.....but that is a lot of pack otherwise. They say that more because the Metcalf is all you need up to a week, you could suck a Marshall down and be fine. Just depends on if you want to carry the extra weight all of the time. That is a screaming deal for sure.
It's like a 1 pound difference, but yes, a lot of pack.
IMO, the biggest thing is you got your hands on that frame. Worst case find someone who wants a 6500 bag and find a used Metcalf. I purchased my Crewcab 7 years ago, and since found used Longbow and Metcalf bags. I still use all three, and they are a breeze to swap out. I generally hunt with my Longbow or Metcalf and then switch to my crewcab for hauling meat. One of the best purchases I have made.