I'm currently running a 4 drive RAID 5 array of red drives. I'm in the middle of encrypting them using true crypt. Now the bad part.
A new 2 TB drive, 64 MB cache, on an Intel Z77 chipset (SATA II) maxes out at 15MB/s in the array. The highest access speed I got was about 20 MB/s. I'm looking at 4 days to fully encrypt the array.
Note two things. It's supposedly a SATA III drive. Z77 obviously doesn't offer this configuration (in RAID at least). The second is that I'm running a stock clocked 2500k. More than enough arse to do all the heavy lifting and remain below 28C on each core.
Can I recommend red drives for your OS; no. Can you get away with them; probably. Has having a SSD spoiled me terribly; absolutely.
You haven't seen anything until you've seen this.
Wow! I didn't know the blue screen of death could get a blue screen of death.