I have been looking at the WP / BMW EDS for my 07 12GSA, but haven't decided yet. My understanding is that they fit the GS, but would lower my GSA (to GS height). Please post all info if you decide to go down that road.
I considered doing this but was advised by suspension experts MCTechnic that 1) it was very expensive to do properly (they reckoned over £2000) and 2) was not worth the extra over 'ordinary' WP stuff. In the end I fitted WP spin units front and rear and have been delighted with them. These have adjustable rebound, high-speed and low-speed compression damping as well as length and preload. The adjustments are very easy to make with an allen key but I didn't bother with the extra preload knob as I seldom carry a pillion.
Ride and handling are both greatly improved and I prefer them to the Ohlins I had before.