12 HDDs? Mother of god....
As for slowdowns... well, just imagine how many times those heads have to move on the platters....
I have 4 HDDs which are partitioned resulting in 12 HDDs. They are not all used and I really don't need that much storage. My Primary disk is SSD. Am I slowing up my computer by having so many hard drives???
I think it will dramatically slow boot times
My OS is W7 64bit, Main drive is 120GB SSD, Asus mobo P8Z68-V Pro/Gen3, Intel i7 2600K 3.4G, 8MB Ram.