Board Thread:General Discussion/@comment-24903391-20140506235936/@comment-1466854-20140711131552

There are some exceptions to the 10-level rule, depending on which spirits, which stats you care about, etc. If you have an SR spirit with awful speed but high hp and attack at level 55, maybe you won't max speed's bonus by level 65 when you're pure merging. But then, because it's speed, maybe you really don't care.

Personally I started my greys and ah puch at level 35 due to their pitiful speed values, but that's mostly because I get so many of both that it doesn't bother me wasting a few if need be.