MBP Mid 2012 HDD for Optibay SATA II or III

[Giblp59]

Just bought a SSD (Samsung 830, 256 GB) for Replacing Main Drive.
I plan to buy a caddy and a 7200 rpm for the optibay (Don't need the DVD Drive).
Do I have to buy a Sata II or III HDD?

Seen these so far:
Seagate Monumentus (SATA II,III available)
WD Scorpi Black Sata II

Something to look at by buying a caddy?

I have the new Mid 2012 MBP (Non Retina).
I'd put System and Samples on Main Disc SSD and Audio Recordings on the 7200 rpm drive in the optibay. Better Ideas (I'd like to avoid external disks)

THANKS!!!