I would like to indicate here that I seem to have solved this problem. I am not sure which of the things I did solved it, since I have no patience and did them all together.
I have an ASUS Crosshair Dark Hero VIII motherboard.
1. I updated the bios to the latest version which was released less than a month ago.
2. I updated all the drivers and software the motherboard came with.
3. I installed GameFirst VI, this is a Asus utility.
As you can see there is a drop in framerate just when the bombs a drop, but then goes up again, until the bombs get close to the ground, then it drops again. Note sure why, but at least it is playable.
Spectre VCAW-1's post in Performance hit when a large number of bombs are dropped on AMD was marked as the answer