Sitka flash 20 vs. 32 vs. bivy 30

[jgt24]

Anyone have experience with all three of these packs? I'm wondering if the 20 is big enough for all day back country hunts.  I have a buddy who uses a bivy 30 which seems to work well but I wouldn't mind something a little smaller.  Also does the 20 have an internal frame like the 30?  I guess I'm just trying to decide if 2000 cubic inches is big enough or if the 30or32would be better.

 

[Bullhunter]

I use the Bivy 30 but its just too big for a day pack, now with that being said it works great as well a Bivy hunt pack.  Im looking at the flash 20 but i havent pulled the trigger yet