Luke apparently both the Simms and Patagonia zip ups are 100% waterproof...
Granted I wouldn't want to load them with $10000 worth of camera gear and swim them to 3 metres deep and leave them there...
But as a waterproof pack, that you would be wearing/using on the flats or an open boat in rough seas etc, where it will get splashed a lot, or even completely drenched ( surf fishing, or swimming across a channel whilst flats fishing ) they are perfect..especially if you need to access the compartment to get stuff regularly... thats where the roll tops fall down in my experience... they are a nightmare to access anything whilst standing in knee deep water... Only draw back I can see is they don't have a Hydration/bladder pocket which is kind of essential for flats fishing in my opinion..
That Core Pack looks pretty bad ass as well..