I am totally biased on this subject, but it is with at least a modicum of scientific basis. I have mentioned this before, but I had Joe Stimola from Penske Racing dyno all of the Vincent shocks I could get my hands on: Koni (predecessor to Ikon), Armstrong, Spax, and Thornton (Works Performance). He said only one was suitable and that was the Thornton. He was stunned at how close the graph was to a Penske shock graph. The closest performer was the Koni, which was some 300% out of the correct range.
In the real world of daily street riding, most riders simply do not find that there is a need for excellent damping. I would put myself in that category. Most of my recent riding was on the track and I would only use Thornton's. In some ways I think that you can now get the damping that you wish to pay for. A friend recent purchases some Ikons and I was not impressed with them, but he was happy.
You do have to change the oil in the Thornton's. If you are unhappy with the performance I believe Works Performance will rebuild and also re-valve them.
I understand that the original shock can be made to work well with some modifications, if you still have them.
I have never seen a performance graph of Rob's shocks, but Rob is very knowledgeable.
David