John and b r Thanks for your thoughts. So are you saying that the decrease in angle that the cups provide provides just as much additional stress as a longer fork that generates the same angle. 

Or that because of the additional travel your more likely to do something beyond the original design scope for the bike and potentially put to much stress on the frame?

As you say pretty academic give the tolerances of the frame but intriguing me as Giant has now changed the head set angle by 2 degrees and I can't see the difference between headset cups doing the same. Unless theres an implicit trust in the original design being fit for purpose (I used to ride crack-n-fail so I'm a tad cynical).

b r pretty sure it can take the forces- my basic engineering tells me that a 2 degree change in head angle won't increase the forces by 2%. The tolerance built in for handling people weight means that its weigh within the force spread (NB. I'm not exactly heavy.  I don't take things on at reckless pace any more - hurts too much when it goes wrong when you get to 50 . Won't jump it other than the occasional short hop). What I want it to do is be able to handle the trail centres a bit better and I worked it out on my last trip to Coed when I swapped from my all mountain rig to the Trance.  I felt too on top of the front wheel and kept fearing it was going to stutter - didn't but I had to work hard. Then rode it back here on my usual trails and whilst its tight and snappy I just felt a slacker head angle would make it all much more relaxed.