I've actually watched a vid on youtube where the poster was using the console to pit a deathclaw against a behemoth. They fought several times, but I don't recall seeing the behemoth win a single fight. Simply put, the deathclaw and its attack were too fast for the behemoth to cope with. It always resulted in the deathclaw getting in the first shot which interrupted the behemoths attack.

For the note, Fallout 2 also had geneticaly modified Deathclaws that was par on with human mentaly.

Now there's something Bethesda should have considered putting into the game for giggles, random creature mating scenes.

I believe those ones were genetically modified by the Enclave, FEV or otherwise.

Is it ever explained how they become the creature they are now???