By the time you get the money to buy two of those for SLI, they'll be way outdated.
In several years, we'll have 8 core CPU's, 16 core GPU's, quad-core physics processing units, quad-core sound cards, 500 TB hard drives, 16 memory slots, PCI-e x32, fusion powered PSU's, cooling devices that work by teleporting heat to some random place in the world, levitating cases, wireless everything, 5 inch by 5 inch motherboards, tiny CD/DVD drives with tiny CD's and DVD's, controlling computers with your brain, 20 Tbits ethernet, and a whole lot of other crap that nobody will be able to afford.
Wait... paying?! Screw that, I just wanna STEAL.