well, my computer run 4x4gb memory..
And it seems a little bit more responsive when i was run at 2x4 gb rather than this 4x4gb..
More banks need more power processor..
go with the highest frequency you can go..because memory is investment..
if you go to the newer systems later, you can keep this memory.
Ddr4 will became majority at 2016 or even longer, so don't worry. your new ddr3 memory is not out dated very quickly..