All I can say is Big_Swede made a very good point about people on this site and their big green sacks. Depends what you are using it for. Carrying loads of heavy gear short distances from the car, landy or van to a wood camp / moot spot then very well. If you have to carry all your gear in one bag over many miles while backpacking then I do think you have to account for why you are carrying up to 3kg in a sack when there are sacks available that work just as well in the real world weighing 1kg or even less depending on your load weight.
IMHO the big green sack does not offer any benefit in what is perceived as its biggest selling point and that is durabilty. I have used sacks and most definitely abused them for many years and have not so far damaged a sack. I have used some UL sacks weighing 600g and found them perfectly adequate for backpacking use. I scramble, climb and throw them around. I trip, stumble and fall on them. Sit on them and even been known to throw them down on the ground in a strop.
My point is the bergen type of sacks are an old technology now. They are a little bit from the time when it was thought thicker fabric, more webbing and more stitching makes it a real tough sack. There are better options out there but they might not be the big green or black SF sack/bergen. You are not a bulk, contract buying military body so why get the type of stuff they get limited with. Afterall it is not uncommon that some units allow them to buy their own, better stuff.
I personally think the newer products inspired by the USA's UL backacking community using dyneema and some amazingly tough but light fabrics is a better choice for backpacking. The Crux is known as a bombproof sack. If you rip one of them you are a cretin. That make of sack is tougher than the bergens. It is the simplicity of it that makes it particularly tough. A single compartment body of the sack made out of as few pieces of fabric as possible, with good stitching, webbing and buckles, etc. They all contribute.
Now as an outside bet try Aiguille Alpine. Based in Stavely in the Lakes they make their own sacks above their shop. They offer a degree of customisation all in their standard price. The sacks are cheaper than main stream brands for what they are and there is no fuss with them making them reasonably light. If you read through some threads on here you will find out that people tend to keep this make and use them for decades. They are known as being well made and very durable. I like the fact that I have got aa back length made to fit my back not the "standard" back size whatever that is. I think it is also another good sign that MRT members use them as do climbing guides and I believe some military units (if he's not spinning me a yarn). You just have to get over the big green sack herd mentality.
Sorry if I've been controversial with my big green sack comments but its just my honestly held opinion that those sacks are attrocious for backpacking use when compared with what is out there. There are some reaally good sacks that people are ruling out for what appears to me to just be a question of colour.
