
Thanks to everyone who talked through this problem; it really helped me. I've balanced all (and brought all to mind) and finally plumped for the Jam. I picked it up from 1Outdoors.co.uk a few weeks ago and I have to say I'm very impressed - with everything! It seems fairly huge to me (the Gust must be massive - what on earth must people pack?), but when compressed down it's filled in nicely as a daysack in that time. Better though, it's replaced my 60 litre backpacking sack for fast and light weekend jollies. Less capacity means I pack less, packing less means it weighs less, weighing less means I go further/climb higher/skip and jump around more. I can highly recommend the Jam then - I guess I'll wait until winter to see if I'll need the Gust.
More importantly I must mention how great James at 1Outdoors is - the very best customer service I've experienced from any retailer anywhere; web, outdoors or otherwise. Huge kudos to him and his excellent website.