Clock speed would probably be a big factor, but the way I see it, why try to pump 16GB through two slots when you can do it through 4?
OP isn't skimping out on the motherboard so I expect full speed (whatever that is) across all four DIMM slots.
Also, $300+ for PSU? I thought $150 was plenty haha.
I like Anfanee's list, except I'd swap the GPU with MSi (I like their cooler) and the Corsair CPU cooler with a Gigabyte (I had a 140mm Hydro forgot-the-model and that leaked, although it was crammed into a tiny case, but still, 'loose' connectors on the block).