I can update the picklist limit value in the Impromptu.ini file, and it seems to be working, but why does this value not show up in the Configuration Manager? I am using IMP v7.5 and the user with the problem is on IMP v7.3.
I don't think the picklist limit was added as an editable option in Configuration Manager until one of the 7.4 releases. Prior to that, the only place that I'm aware you could change it was in the impromptu.ini file.