Stoicism

[Angrboda]

I think the Stoics, like all schools of philosophy, derive their ethics from their metaphysics. Basically: the world is this way, therefore you should behave this way. 

In other words, if you ask a Stoic why you ought to live according to his ethics, he can give you strong reasons. Much more than just "this sounds good to me." 

In fact an emphasis on practical usefulness is probably a very modern thing. So choosing a set of ethics based on what seems useful would go against the original Stoics. They would say you ought to choose your ethics based on the the truth of the way the universe is. 

I used to read about Buddhism a lot too, and spent some time at a Zen retreat. But in the end I stopped because I couldn't accept their metaphysics. Granted, if I had continued to meditate seriously I might be better off psychologically right now -- but that would make Zen practices into mood therapy rather than real Buddhism.

Arguably though, the original Buddha (Gautama) did not focus on metaphysics at all.  In fact he is quoted as saying that worrying about metaphysics is like being shot with a poisoned arrow and demanding to know where it came from, rather than focusing on getting it out of you before it poisons you.  Most of the metaphysical ideas of Buddhism come from the pre-existing religion of Jainism.  The Buddha's highest priority was to eliminate suffering rather than answer questions about the supernatural.

The Buddha also said that up to a certain point, you needed the raft to get you across the river.