I'm pretty sure the Colorado 5-spokes that I used to have were -15 offset Jon... And you are certainly right about the 80 alloys being zero offset.
As the 80 alloys 'stick out' more than the old Colorado alloys on our 90, extrapolating (sp.) this logic, wouldn't this mean the -25 offset rims would be further under the arches rather than out???
I'm in danger of serious confusion here not knowing for sure which way the +/- moves the wheel