its like two individual drives, one for /etc the other for /usr
and no, you cant have half the latency, latency is dictated by physical speed of actual ram inside chips, those are clocked at 200MHz for typical DDR3 1600Hz module, up to 300MHz for fasters DDR3 ones.
Actually it's more like raid0 than separate partitions, because anything upstream of memory controller does not have to care about this in any way. The amount of complexity between modern CPU and memory is quite fascinating (and huge amount of essentially invisible and relatively complex stuff is there at least since i486, i.e. with anything that does not care, in the works/does not work sense, about how you combine memory modules).
its like two individual drives, one for /etc the other for /usr
and no, you cant have half the latency, latency is dictated by physical speed of actual ram inside chips, those are clocked at 200MHz for typical DDR3 1600Hz module, up to 300MHz for fasters DDR3 ones.