CS5s. The difference between the 5 and its 'improved' version is that Jim's newly developed woofers weren't ready when the 5 had to be released. The improved woofers incorporated copper shunt rings for more stable motor response. Those i woofers are not available (as far as I know). Nearly all 5s in the field are 5i conversions. The 'i' drivers have MDF mass plugs instead of the 5's rubber cone mats.
In my recent minimal recordings I used CS7.2s as site monitors. Very nice. My studio has the CS5i, which are overall less articulate and nuanced, but their coherent bass alignment makes them more real to me. My invisioned CS5.2 will have a sculpted baffle for proper driver placement, thereby eliminating 32 elements for analog delay on the 2 midrange drivers.