Its not particularly long load times however basically doing anything in the background like opening up a browser, starting music or hell just using some the crap in the steam overlay will basically exponentially increase your load times. GTA 5 is not the greatest of handling interference with background processes.
you only put the most used files in the ssd and then make a notepad file saying that the files are in ssd. I'm not really good at explaining it but it should be something like this >> (this is for bf4 but you can use it for any other files/games as well) http://www.reddit.com/r/battlefield_...drive_ssd_but/ and search things like "how to install games on two drives"
This is a really sweet thing. Wich files from gta v are the most used tho?