Do a little research on long term use of SSDs. I believe they may have a limited amount of reads and writes (although, obviously, since they are already used on many new laptops this is either a large number or they have overcome previous limitations, but CHECK).

I think whatever allows you to use the laptop at greater speeds should be your C Drive. Audio and Video files will not gain much by higher random access as they do not require much random access (they are large typically contiguous files).