I use Koni sport (yellow) on my spider.
I think that it isnīt too stiff. You can regulate it and then you can have a normal shock or a very stiff shock.
Before these konis, I had the koni special (red), and really, they are no too much stiffer.
The pink area shows the adjustment range where both shocks are equal in value.
A friend of mine has on his Spider serie 4 the koni sport, adjusted at maximum.
Also, I think that Bilstein (gas, konis are oil pressure) are a good option. I have a toyota equipped with bilstein and I am very happy with them