The rtm may be an option, but you won't know till you try and have plan b in place.
I couldn't make our Festae co-habitate with a female Rivulatus (GT) in the 300 so you're already better off than I was in that regard.
Salvini and motas end up around the same adult size so it'll really depend on the individuals.
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Doesn't the Mota get 3-4 inches larger than the Salvini?