SheepDog,

I have both. I just started playing with the Fatboy Jumbo and I'm still on the fence with it. It is nice for holding a Nalgene bottle and does have alot more room than the standard Fatboy, but then again, bigger and heavier. I use the Maxpedition Thermite Versipack as a leg rig for basic survival items, so it is always with me (I switched it from a right side rig to a left side rig by switching the straps (a little sewing involved). I also removed the outer pouch to make it thinner for wear on the leg.

But back to the Fatboy Jumbo. It is very spacious, but again I'm not sure if it is TOO big. Still playing with it and will report further.

Fox10