how strong are they?
Incredibly so. These are the pitons that made Black Diamond, back when it was just Chouinard making them himself out of the back of his truck. There is no way in hell you will ever bend or deform these in an kind of climbing application.
You can bend and deform these from regular big wall use. Hammering them in and taking them out will definitely put some wear and tear on them, but they will stand up to alot.