Look at it this way, why would you want to lose weight so fast? Everyone I know that has had gastric bypass has gained half if not all of their weight back.
With gastric bypass, if you stretch your pouch, there's no shrinking it.
Lapband, if you stretch it you can shrink it
Keep all of that in mind.
By the way my BMI was over 40 and I'm happy with the weight that I've lost so far.