I haven't built a computer since Nehalem and pretty much

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I haven't built a computer since Nehalem and pretty much forgot all the complicated stuff. Please discus RAM modules with me.

I see that these days, the average DDR4 module does something like 2133/2400MHz with CAS Latency around 15/17ns, so that's about a real latency of 7ns, right? Now, there's also some hektik gamer RAM with aerodynamic heatsinks doing 3200/3600MHz at CL 14/15ns, which averages 4ns.

Now, of course, smaller latencies are better, but I'm not sure whether or not all that shit becomes relevant at all once in a system? The new SkyLake i7 6700K has on its specs sheet a compliance with DDR4-1866/2133, which is, I suppose the "bare minimum" type of DDR4 RAM it will take, but the part that interests me is the max memory bandwidth rated at 34.1 GB/s. What exactly is this number and how does it relate to RAM? I googled a bit but didn't find much. The dumb thing would be to think well the RAM does 3.6GHz, right? So that's pretty much 3.6GB/s. If I have 2 modules, maybe that's supposed to add up to 7.2GB/s to the CPU? In that case, the CPU has way enough room, so no bottleneck here and the faster RAM really will be better?

Additionally, does the motherboard matter at all for this? I'm under the assumption that all of them have the same buses from RAM to CPU, but that might be wrong. The only specs I found on the MSI-Z170A-G45-GAMING for example is:
DDR4 3600(OC)/3200(OC)/3000(OC)/2800(OC)/2600(OC)/2400/2133 MHz, Dual Channel, 4x DIMMSO, 64GB Max
Which really doesn't tell me anything except that yes, it accepts this kind of RAM.

Please enlighten me as to how those numbers relate to each other. I would like to just buy normal valueram because that gamer shit looks terrible and is not practical at all, but I don't want to significantly gimp my new system either.