Either the 06 SL from Wiggle at £199 or the Race at £249, which one would be best to replace my flexy Duke XC

Either.
Only difference between the two is that the race has an external floodgate adjust and the SL is internal (which you adjust by removing a cap and using an allen key (or pulling out the rebound knob as this has a 2.5mm allen key part for doing this adjustment, clever eh?)).