7970 (x2) => R9 290X (x2) good?

I want change my actual GPU 2x (7970 DCU-2 3 Go)


2x (Radeon R9 290X Lightning - 4 Go) (more info here)

and change my motherboard to a new compatible PCI Express 3.0

Changing card really worth it?
Changing motherboard really worth it? or pci express 3.0 is joke?
password cracking does not benefit from PCI-e 3.0.

going from 7970 to 290X will be about 35% faster.

Check it out.

Is it faster? Yes.