It will work and your performance will be better than just 1 260x in most cases, but yes, with the one running at 4x, you will get lower performance due to the budget quality of the motherboard. i would highly recommend a better motherboard with at least the possiblility of 2 8x lanes before you decide to crossfire. otherwise just buy a more powerful single gpu and forget about crossfire. honestly my recommendation is to forget about crossfire completely, as with dual card solutions you tend to run into power problems if your psu can't handle it, and not all games scale with two cards.