Total: $505. The board is quite a bit more expensive, but has USB 3/SATA III support even when Crossfiring, which others might not. There are several cheaper ones out there if that's above your budget.
your right, it doesnt really matter, but last time i checked...1.35<1.5, so the eco can acheive a higher oc, without raising latency...so the eco can probs make it to 1800, and 1.65, and the 1600 mhz can probably reach 1800 at 1.65 volts, so both are good, but i would rather the lower voltage. also, there is a 1600 MHz: