6112s are a coilover only, no rear shocks will be made. Youll need to go with either a 5100 or the 5160 w/ reservoir. The 5160 rear is a tad longer than the 5100 to accommodate a larger lift block or add a leaf.
The performance and ride quality of the shocks described above is as follows. Bilstein 5100 < Eibach Pro Kit < Bilstein 6112. Its hard to compare the 2.0" diameter of the 5100 and the Eibach kit to the massive 2.65" diameter of the 6112. The larger shock size means the 6112 has 40% more dampening force than the 2" shocks do, which means it doesnt have to work nearly as hard to absorb an impact. The Eibach kit rides slightly better than the standard 5100s as it has its own coil spring and is tuned as a package. The 5100 is a major upgrade from the stock Rancho or Tenneco shocks in terms of ride quality, as mentioned in this thread.
6112s are $610 here - http://mrtmotorsports.net/bilstein-shock-sets/bilstein-6112/47273702/i-7474057.aspx