How many times must I fight 3bp Ibaraki.

Well, 300M/1M = 300 x 2 BP so 300 times if you are going to do the 2 BP.

300M/6M (if you can deal the whole 6M)= 50 x 3 BP.

If you can deal more than 1.5M on the 3 BP and survive the 15 turns, that is more efficient than the 2 BP node.

Generaly, 2 BP for farming Demon Gourd and 3 BP for damage points (if you can do it on a stable basis).