RPM and cache size aren't anything hidden.http://pcpartpicker.com/parts/internal-hard-drive/#m=34
All right there in the list.
Here's a bit more filtered list. http://pcpartpicker.com/parts/internal-hard-drive/#m=34&t=7200&f=2&c=64&sort=a10&page=1&S=1800000,2000000&i=25
That is all 2TB, SATA, 3.5" Seagate drives.
The difference is the series, and whatever benefits those bring, which I'm sure google could give you a decent answer. I'm not familiar with the Seagate series as much as say WD.
They have Green, Blue, Black, Red, Purple (and maybe some more colors now)
Green-low RPM, eco friendly, not full time access kind of drive.
Blue-Good speed, good performance, ok warranty.
Black-5 year warranty, generally the best of the comsumer ones
Red-For NAS systems, generally optimized mostly for reading over writing. Having the entire simpsons on your NAS to watch, 99% of the time, it's just read.
Purple-For security camera recording, optimized for mostly writing. 99% of the time, security footage is recorded and never watched so the drives are geared towards writing.