So digging around the forum I found a few posts related to the min curve rating. Seems like O42 was unrealistic, but O54 seems to work fine. It also seems to depended on S-curves and the coupled rolling stock. My layout has an O60 minimum and I only use the skeleton cars I have. Although Barry in the posts/threads I’m linking below has run some more typical cars behind his shays on O54. Any way, after reading that folks seem to be ok them depending on rolling stock, I’m going to get one.
here are a couple of the posts I found:
