Yes, 90mm should be about right. It looks as though you have the original stem ATM, but the fork that was on there was 2cm longer than the original fork. I find that a 2cm shorter stem compensates for a 2cm longer fork - and that seems to be the way that Kona have developed their design over the years as forks have got longer. But original stem with 2cm longer fork has to make the steering less lively than it was originally. The fact that the Pace is an excellent fork, and far better than a Z4, is part of the reason why the handling already feels fine of course.