Does anyone know what is the bare MINIMUM size you can get away with when rewigging an AG?

I found the wig I need, the color, cut, EVERYTHING to replace one with a really bad haircut. But it's at an online store and it only goes up to a size 9-10. Would a 9-10 look really weird?

Has anyone actually used a 9-10 without it looking freaky?

The color I need is EXTREMELY rare, and I don't think I will be able to find it bigger. (actually I've only found one that store that has this wig at all)