As promised I've taken a closer look at the bag. The hip fins are easy to remove being held by Velcro tabs, double sided means a secure attachment but I'm still wondering about how well these will work with loads when approaching the claimed 30lb maximum.
Golite's rucksack ideology goes back to Ray Jardine who wasn't a fan of hip belts for the simple reason that if your load is as light as you can make it hip belts are effectively redundant. And since a lot of weight in rucksacks is the hip belt and back system it makes sense to strip these out or pare to the minimum to save weight. That said I still feel that even with lighter loads some transfer of weight to the hips is essential. It lowers your centre of gravity adding stability, and if you're running, jogging or scrambling then a hip belt will keep the load from moving about. From a personal point of view I won't bother to look at a rucksack that doesn't have pockets on the hip belt. Removing the hip fins will save 133g.
As stated the foam back insert is removable and can only be done if the 'sack is empty, and even then it's a struggle to get out as it fits tightly. I ran the foam under a tap and although it doesn't look like closed cell foam it didn't take up any water. If you use three quarter length mattress or pad then the bag can be put under your heels if required but I wouldn't bother going to the effort of taking the insert out. The foam insert weighs a measly 44g.
With the hip fins and back insert removed the stripped down weight is 586g.