This whole suspension thing has been a bit confusing to me, so I thought I would do some research, and then present what I found. Please clarify/contradict as you see fit.
First, GM categorizes the parts that make up a vehicle. These parts are broken down into RPO's (REGULAR PRODUCTION OPTIONS). Thus the FE4 and FG2 codes we use to identify the type of suspension and/or suspension components found on the CTS-V.The RPO codes for the CTS-V can be found on the FAQ:
These both list the stock CTS-V suspension RPO as FE4: Suspension, performance tuned
They also list the FG2 as: Regular Production Accessory, Performance Shock Absorber Package (SPO-supplied, dealer-installed)
The optional FG2 Shock Part# 12499241 The optional shock package for the CTS-V which is more "track" focused and supposedly rougher. Load Leveling (nivomat). (GMpartsdriect.com)
When it becomes confusing is when others use other RPO's to describe suspension components. Perhaps the underlying part number are the same, but the RPO's are different. In a few other threads the RPO FE3 has been described. This appears to be the sport suspension for the regular CTS, and also the Z51 suspension for the corvette. I could not find this RPO anyway associated with the CTS-V.
By the way, there is an interesting thread going on over on the regular CTS board about suspensions and how they interact with the Eibach spring kits. Specifically they talk about the FE3 suspension, for the regular CTS. (http://www.cadillacforums.com/forums/showthread.php?t=26716&highlight=fe3)