I noticed the WD Red drives only got reviewed on release and not since, whilst that might seem fine, I brought 2 drives last week which in terms of spec and performance are significantly different to my 2 year old RED drives, all 4 drives are the same 3TB.

According to AIDA64

Differences include but not limited to.

Old drives

NCQ supported
Accoustic management enabled
4k advanced format sectors
Security supported (not sure what this is exactly)

New drives

No NCQ support
Accoustic management disabled
512byte sectors
No security support

Performance wise the new drives are way faster.

Also the new drives have more statistics available on SMART data.

Across all 4 drives I have 3 different firmware versions.

The 2 older drives are v80 which many on the net have.
The 2 newer drives surprisingly do not have matching firmwares, in addition one drive has more capacity than the other (an extra gig), and I havent found the firmware version anywhere on the internet reported by anyone. This size difference makes me think the 2 new 3TB drives have different density platters to each other..
Also the 2 new drives run 10C hotter.