Samples & Audio on a single SATA III or Audio on Sata III and samples on external USB 2?

Hi all,
I'm wondering how to place the files on my new PC build.

I have:
1) 160GB for windows & apps
2) 500GB Green WD for files (I think it's too slow for any involvement with the DAW)
3) 1TB Black WD Sata III
3) 500GB Samsung USB2(external) - it's a lil' old...

I'm wondering if I should place either audio or samples on the external samsung instead of keeping both on the Black WD Sata III.
I know that normally it's good to seperate the samples and audio but because samples go to RAM when you start the project and the SATA III is much faster than USB2 I think it would be best to use the external for general storage and keep both on the Black WD.

What do you think is the best way to go?

My only comment here would be to have the stems on a drive other than the boot drive...the faster the drive the better as track counts and processing escalates...