I don't think the CPU will bottleneck 2 770s. The 8320 or the i5 will both be fine with no bottleneck . games aren't largely CPU dependant still. Their bottlenecks lay in the GPU still before the CPU. With two 770s he woulnt have to upgrade for many many years . assuming games and game engines continue to move towards heavy multi threading (which it appears they are). Plus over time I think well continue to push certain aspects of processing a game into the GPU (and lighten the CPU load ), kinda like how nvidia has PshyX set up.
A new CPU and mobo might have small gains but not worth the costs that's for sure. It could also mean you need a new copy of windows to go with it too..save the Intel for the Glnext big build. Start saving up...