How to calculate how much data a Core 2 duo E8 can write to the RAM per second?
My first question would be: which RAM? Do you mean one of the L1/L2 caches (those are pretty quick), L3 or worser still: memory RAM? 

Possibly of use:
https://panthema.net/2013/pmbw/results.html

You also grab the utility here and run it yourself.

Notice the enormous differences between "cache" and RAM bandwidths. Such differences also translate to random access latency as well.
Modern high-performance computing is all about hitting that cache as efficiently as possible, because going down in caches or back to main memory is a massive slowdown.