1) Do a Googlesearch on the memory chips
2) The thing is that 32GB of 2400MHz memory is just as expensive as 64GB of 1600MHz, so is it worth it?
Twice as much memory is p[robably (not the word probably) more important. Depends on what other programs you are running on the host. 5 instances of Photoshop for example might require more memory rather than more speed. 
For myself I'd go with 64GB of memory - BTW what mobo are you using that t can support these many momory sticks.