Nothing beats a set of Bilstein Sports or Konis with off-the-shelf sport springs for simplicity. However. at higher spring rates, Koni Sports ( "Yellows"), or custom valved struts/shocks are the only way to go. I used the Koni Yellows for a while, but now I have a pair of koni 8610-1149 struts in the front.
The Koni inserts are shorter than the stock style struts so I made a stainless spacer for inside the housing. The spacer diameter is important becasue the spacer should not have too much slop inside the housing. I put a tapped hole in the top of the spacer so I could use a piece of threaded rod to pull it out it it got stuck. I also hogged out the bottom of the spacer to save weight. Steel or stainless should be used instead of aluminum for strength reasons.
The 8610's use a larger diameter thread at the top of the strut rod, so the stock strut bearings definitely cannot be used. Camber plates are a must.
After beating myself with a scanner for a few hours, I finally was able to generate some pictures. The photo above shows the yellow Koni Sport strut and the Koni 8610 strut insert. The standard Koni struts for the E28 have an M14 thread at the top of the strut rod but the 8610 has a beefier M16 thread. The additional reduced diameter at the top of the 8610 also makes it easier to design a camber plate. The tall stainless steel cylinder is the spacer needed under the 8610 insert due to its shorter length. I hogged out the underside of the spacer to save weight.
This shows the significant difference in length between a stock style strut and a semi-universal insert. The spacer length is critical because Koni specifies a specific tolerance on the gap between the strut housing nut and the top of the housing.
I decided to put a tapped hole in the top of the spacer to facilitate removal in the future. If for some reason it won't drop out of the housing, a piece of 1/2-13 all-thread will pull the spacer out..