Hmm, the dollar pound price thing isn't as bad as first I thought, Amazon.com is selling the Rush 72 at the pound equivalent of around £110. Significantly cheaper than Amazon.co.uk rates but still, not as bad a price difference as I thought.
I suppose it comes down to horses for courses. I spent 20 years in a busy MRT and the favoured bags were big and simple with no 'designer features' which limited flexibility. I suppose I'm conditioned by experience; for me, molle is still something of a novelty and simplicity a desirable virtue. I've learned not to trust zips, though the self healing zip is a big improvement over the earlier heavy duty metal ones.
I can remember times when we were out in continuous torrential rain for days on end and I'm not convinced any zip would have kept rain out under those conditions, but I suppose a sac cover would keep things fairly dry. I don't remember anyone ever using one though. The layout of the Rush is novel to me but I can see that service personnel would possibly sometimes need to be able to lay open their sac contents for access, fair enough, but having a potentially leaky pack nearly double the weight of a Centurio is a heavy price to pay.
I wonder if you need 55L for 3 days? Yonks ago I soloed the Pennine Way in 10 days using a Karrimor Hot Ice sac at about 25/30L, wild camping/ bivouacing & picking up grub on the way, apart from my high energy home brewed muesli. Admittedly early spring but it was perfectly possible. For a 'survival' situation you need basic kit and lightness on your side: a fully loaded all situations big bag can slow you down and -worst case- exhaust you. Obviously you'd need a bigger sac for winter, horses for courses...
Right now I'm working on slightly modifying a Helikon Wombat shoulder bag (about 20L) so that I can use it as a day bag which will let me walk around without attracting attention as a walker but which will carry enough for a relatively comfortable night if need be. As I say, horses for courses: first define your needs, then set about meeting them.