Osprey are nice if a bit expensive.
Are you sure you need 65L? I'd try to get my kit down to less than that if possible, 65L of stuff weighs quite a bit even if the individual things are light.
Best advice is to try as many bags as possible though. It's no use the bag being technically brilliant and made of fairy dust if you can't get it comfortable.
Everyone is different. Main thing is to get a bag that fits your torso length. Getting it fitted in a shop is a good idea.
Due to current wee problems with my back, I've invested in an Osprey Aether pro 70. Excellent. Fits like a glove and can be stripped down and cinched for smaller loads. Very expensive though.
That is for long multi day hikes carrying food eyc. Usually you can get away with a 60 litre. I also have a klymit motion 60. Lightweight, good load carrier and comfortable. However it is not adjustable for torso so hit and miss.
For 1 night I've managed with a 40 litre.
Best advice is for you to get your gear and see what it will pack in to. A 50 litre bin bag or a 60 or a 65. Then go and try on packs in that size until you find one that suits. Don't try them on empty. A good shop will put stuff in it to give you an idea. They will also measure you.
As Sean says, don't get a massive bag if you don't need it. You will only try to fill it.
As above it is imperative to try on various bags to find the most comfortable. Go to a mountaineering shop with experienced staff, not one of the big chains that sell everything to do with sports.
We got ours fitted at Tiso: all the straps adjusted so weight was taken on hips not shoulders & balanced so the weight wasn’t tipped back. Got advised on how best to pack them too (don’t ask me, too long ago).
Got to agree with all the advice so far, I looked at so many a few years ago, didn't matter how technically good they were, or price within certain limits, I struggled to find one that fitted at all, let alone comfortably!
OK I've got wide shoulders and a big chest, but there were bags I couldn't even get on simply because the straps didn't adjust far enough, others ended up with shoulder straps that dug in as attachment points too close together for my width, really began to despair, ended up with a mid range one a bit below the quality/price range I'd been looking at, simply because it was the best and most comfortable fit!
You really cant buy by specification alone, every bit as much need for a good fit as there is for walking boots!
I found my Osprey Exos very comfortable but I'm a bit ocd with packs & found it a bit fussy & I struggled to close the zipped pockets on the hipbelt. I replaced it with a UK made Atom Packs Mo 60L. As I went for the custom option which is non returnable (except for faults) I had a fitting appointment at their small Lake District unit. Very pleased with it.
As others have said I'd recommend a visit to a decent shop for a fitting.
I am in the same camp as Ewen, I also have the Osprey Aether Pro and it is simply the best out there. You will not go wrong with any Osprey rucksack, but as already said, get yourself measured, and, as I am sure you already know, the weight goes on your waist band, not your shoulders. Living on the Two Moors Way, I see so many people hiking with the waist band undone, hence all the weight on their shoulders. Just don’t!
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