Get 2 x GTX770s instead. Crossfire has to many issues. Unless the software he uses favours AMD, which is doubtful.
Powersupply is a bit much. 850W is more than enough.
No one can tell you right now how long it will last, but 3years should be safe, things are changing in gaming, and fast. Personally I believe we are gonna see very few development in gaming tech for a few years. So may last longer.
Value? LOL not really no...
That Sabertooth board is pointless, there are better and cheaper option and the heatshields are actually a bad idea.