it will work, but be aware that both will be working at the smaller memory, so both will be at 1.5gb that is ok for low resolutions but if you are playing with multimonitor 1.5gb may not be enough.
also their clocks are slightly different it is recommended to synchronize both, i think that the Matrix can handle a slight overclock to match the 580.
Basically the performance will be awesome, but for multimonitor systems you may be bottlenecked because of the 1.5gb so in some situations the single 580 classified at 3gb can perform better because of the VRAM that is the major problem other than that the performance will be awesome.