Hi Daz,
I have just gone through the task of re bushing the front end of my cobra. I used a medium softness Urethane supplied through Jag Spares here in Melbourne. (These are not the Nolathane brand). I chewed through a set of rubber bushes in a very short time ~ 2 years, but I think the track work did most of the damage.
In comparison the urethane has been the best thing I have done to the cobra. The ride softness is exactly the same as it was with the rubber bushes (It would be very hard to tell the difference), but the steering is now far more precise. You can an even softer set of urethane bushes from "Lovells" suspension components (
www.lovells.com.au). They have three grades of urethane.
If you buy the rubber bushes, which appears you have already, make sure they are genuine OEM rubber replacements (They will cost substantially more). The cheap rubber copies are just no good.
Cheers
Tony