[quote=Sho Minazuki]
Usually at around level 40 your initial Persona stops learning stuff, because that's when the Ultimate kicks in, or is estimated to.
[/quote]

In P4 (at least) the ultimate Persona has the same moveset, with exception of another character-specific skill. If they stopped at 40 then you'd be screwed if you didn't max them. You might be referring to P3, where thry auto-evolve, but even then I believe they have the same moveset.