| Just been looking at the 2005 Championship table and as far as I know only one person in the top ten was running a single disc. Obviously the other nine had the option to change to a single disc set up but decided against doing so. Maybe they prefered having a twin disc setup and there also remains the possibility that the single disc rider may have benifitted from having a twin disc conversion rather than loosing out through having one.
If your forklegs have the lugs then fitting a second disc isn't that exspensive, if the lugs aren't there then it may become a cost issue.
After all you can always revert back to single disc if you find a extra disc causes you problems | 
skidlids
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