Not even Asus themselves recommend using the DirectCU II (or the offspin Matrix) in a dual-card setup on any motherboards following the regular ATX form factor, simply because neither the motherboards nor the chassis are built for handling dual 3-slot high cards. You effectively need to purchase an E-ATX or XL-ATX motherboard, and a chassis capable of fitting such a board not to mention offer some serious ventilation in the expansion card area.
If you're looking toward a future SLI setup the MSI cards are probably the best cards you can get and actually fit into a normal chassis. Do remember however that overclocking a SLI setup is nowhere near as easy as overclocking a single card setup.
I have a thread about it stickied at the top of this subforum, but I can condense it down to modern motherboards not being capable of enough throughput in terms of pure 12-volt current to feed two overclocked graphics cards at the same time as feeding an overclocked CPU.
Granted, the Sandy Bridge platform is quite a bit easier to handle in this regard, a 2500k/2600k running at 4,8 GHz draws about the same amount of power as a previous generation CPU did running stock. Still, if overclocking is your main focus I really can't stress enough the importance of the motherboard.
To be able to push a Sandy and dual Fermis to the limit there are really no boards out there in the mainstream category that will give you good enough current throughput. You're limited to the EVGA FTW or Asus Maximus boards, both carrying the hefty pricetag of three grand.
However, seeing how well two averagely clocked 570's handle with a gently clocked 2500k I really don't see the need to push them any further, and any decent P67/Z68 board can easily deliver enough to push even Metro or Battlefield 3 past the golden bar in Ultra quality.
