Depends on whether the rest of your gear is dialed in really well and how much and what you eat.... 5900 is going to be snug for getting it done depending on the bulk of the rest of your gear. My ex has one and it did pretty well for her, but she wasn't fully self contained either on sheep trips, as she didn't have a tent in her pack.
Personally, for a 7 day trip I would want to be at the 6400 cu in level at a bare minimum. I have used the Sky 7400 for 5 years now I think, for everything from hunting coyotes and whitetails walking out my back door, to multiday sheep trips. The ability to compress a bag down to nothing and then expand it enough to carry the kitchen sink is pretty valuable to me. Zero downsides for me to use it as a daypack.