I've had a couple more trips with the SD Flex Capacitor 25-40L.
Since the BV450 didn't fit in it very well, I grabbed a Contender bear can which fits inside much better. Also, I can confirm the pack does very well with water carry weight. More to the point of the thread though, it makes an excellent daypack when compressed.

EDIT: I forgot to mention that with this smaller capacity model, 40L is really the maximum for this pack. It doesn't have a draft collar, so you actually need to dial in the volume of your gear more than the weight. I chose this capacity because 25L is small enough to be a daypack.