Since this is used for media, raw speed does not matter. As pointed out music requires only a pittance or bandwidth, and your average 1080P bluray rip (16-20Mbps) only need 2-3 megabytes per second of bandwidth.
I would look at the Red if you can afford it, mostly because of the implied durability since they have a 5yr warranty instead of the normal 2 year warranty as well as the increased rated usage (closer to enterprise grade). The Red's have some other features, but they will go unused in a normal Mac Pro setup. At the 4TB price point, the difference is quite a bit more substantial they say at the 2TB range.
I am weary of using the Greens because the fallout *seems* to be higher on the cheaper drives. I have 7200RPM drives in a 5 disk RAID, and they have been running for about 2 years now. They do generate some heat, but it's not terrible. Noise isn't an issue either for me, but I can hear the drives clicking away if the Mac is on the desk while getting worked on.
That's the only concern I have though, is the life expectancy. As stated, for media usage the actual speed of all of them is more then sufficient.
Now what can affect the user experience is Access Times. For movies it's not too bad as you have to wait to buffer the movie anyways and then the drives just sit there and reads sequential for a couple hours. So adding a second or two go find the other movie or spin up a drive doesn't matter. But for music where your shuffling around every song, there is a delay and it can be noticed. For music I totally encourage an SSD, assuming you don't have some huge lossless encoded library. My music library is around 70GB, so it fits on a 128GB-256GB drive no problem. It's one of those things you don't notice until you have it. Also updating an albums worth of metadata goes much faster on an SSD then on a platter drive.
----------
For the ultimate in power sipping though, 2.5" drives are superior. However you are limited to 2TB per drive and they get expensive at that capacity (about $170).
From Western Digital Spec Sheets for "Green" drives.
3.5" Drive
- Current Requirements 12 VDC (Peak) 1.78 A (21 Watts)
- Read/Write 6.00 Watts
- Idle 5.50 Watts
- Standby 0.80 Watts
- Sleep 0.80 Watts
2.5" Drive
- Current Requirements 5 VDC (Peak) 1.00 Amps (5 Watts)
- Read/Write 1.7 Watts
- Idle 0.8 Watts
- Standby/Sleep 0.2 Watts