[ant7]

Cant comment on the different shifters, my car came with the Porsche short shift already fitted, personally I probably wouldn't have bothered, as others have said; the 915 box needs time to shift between gears to work smooth etc, as to the spring upgrade; I can confirm that it is very worthwhile, for not a lot of bother or cost, it just places the gear leaver nicely in the 3rd and 4th plane, [middle] and makes the 915 feel more like a modern shifter, without any negative attributes as far as I can tell, had mine since the first batches from Karsten became available.
As with many things, its down to personal choice and preference, however; from owning these cars for many years now and having carried out many repairs and adjustments over that time, I can say from experience that there is no substitute for accurate adjustment, as far as the 915 is concerned.
Ant.