captain paranoia wrote (see)

550g? pah! that's heavyweight

;-) 

Here's a 120g 52l sack...

I'd go with Matt's advice; get one with the features and fit you're looking for.  And we can't help with the latter.

I had a similar issue recently as I'd found the backsize on my 50L Berghaus pack (which I otherwise liked) had too short a back length for me (although it's great for my wife) and after a fair amount of research threw up plenty of candidates I decided to go with the OMM Villain, as I'd been very pleased with one of their 32L packs.

The Villains seem in pretty short supply but I did eventually get one (the older, orange one) and having used it for one backpacking trip so far I've been very pleased with it. My initial impression of the sack was that I was expecting it to be uncomfortable as the shoulder straps are much thinner than I'm used to on backpacking sacks but in practice it's been very comfortable.

The pack might seen flimsy to someone unused to Dyneema, however previous experience with the material is that it's surprisingly robust.

My 2nd choice would have been one of the Osprey packs.

Going back to the gossamer gear mariposa plus rucksacks. Actually, they are amazingly comfortable. I used mine trekking for 14 days in a row carrying about 6 kg. (I only weigh 50 kg). And it was very comfortable. No problems there whatsoever. I admit before hand I was a little concerned, but it passed with flying colours.

My friend has owned the same one for over 1 year and has been using it on multi day trips carrying around 8-9kg. And he swears by it. Hence the reason why I bought it.

You can carry upto 13 kg with the mariposa plus. And from what I have seen, I don`t doubt that. Gossamer do do lighter ones but I have doubts about there comfort on a 2 week trek.

Having said that, the Z packs do look very interesting. And I will read up more about them. At first glance, at that weight I would doubt there ability to carrying 10 kg or more for example. And how comfortable they are. And the weight of 120 grms does not include the hip belts, which do look very flimsy. Certainly compared to the gossamer ones. 

And at least you can see the gossamer ones in the flesh at Winwood outdoor in Keswick.

As with anything like these, its about finding the right balance between weight, comfort and durability. And knowing what activity it will be used for.

I think the z packs look fine for day walks or over nighters. But certainly not for 2 weeks I think.  

Some of the other stuff on www.zpacks.com looks great!