I found mine to be much better than standard and was worth the investment, they also recommend 7.5w fork oil, which I thought was odd going down a grade with stiffer springs, but the fork action was improved over standard, I think they are possibly over damped and under sprung as standard. Not sure about the spring rates, but I'm probably about 90kg geared up and I was happy id spent the money. Definitely not too stiff.

Thanks!
So I was able to fit the cap but it wasn't easy...

Because of the fine (and 35 year old) thread in the forks, even without the spring inside I needed a couple of tries to screw on the cap.
So you can imagine it was almost impossible to do when applying a lot of force. I was afraid I was destroying the thread with all the attempts.

So I asked someone to help me, and by using a T-bar with a socket, one could apply pressure from above while I could make sure the cap was level. 'Only' took a couple of tries with this method!

Here's hoping the springs are any good (for me) or that I will never have to change the oil....