Some considerations. First, that's a good price for an Arc'teryx Khyber pack; even if it doesn't work out, you will likely recoup most of your investment if you sell it down the road. The construction of these packs really withstand abuse and don't get a lot of wear for recreational use.
Second, what is your purpose? For my distance backpacking I use a ULA Circuit (about 40 liters for the main compartment) and I can keep loads around 25 pounds (food, fuel and about 3 liters of water) that will keep me on the trail for about 7-8 days before resupply (food and fuel) and roughly 100 miles (trail miles). Now this is lightweight backpacking and predominantly warmer months of the year.
With that in mind, you kind of need to assess your kit and season. An 80 liter pack is pretty big, but not necessarily if winter camping/backpacking and you need to pack bulkier insulation. The challenge is that this limits much of the rest of the year unless you just pack more stuff. The problem with large packs like this isn't their size so much as their weight and their ability to compress well on smaller loads. If they don't compress well, then they flop and carry like crap. I've only been able to move down to a smaller pack because my gear has been upgraded over the years...lighter and more compact shelter, insulation, clothing, cooking pot, etc. For those just getting started with basic car camping gear, a larger pack may very well be a good starting point. Additionally, I got the most use of my Kifaru EMR which has about a 120 liter capacity (roughly 7000 cu inches) when I was the pack mule for a family of four backing into a primitive area. Both kids were small and my wife and I hauled in typical car camping equipment (tent, bags, etc.) for our two kids. Thank God those days are long past! My Kifaru is now my winter bugout bag that I would haul to my truck
The Khyber is an overbuilt, quality pack designed to carry large and heavy loads. If that's something that might work for you, the price is pretty good.
ROCK6