I got these numbers from literal back-of-the-envelope calculations, so feel free to double-check.
No element: -25%
Bio: 0% (no change)
No element: 0% (no change)
I tested a few of these with different weapons of different rarities, all received the same bonus / malus.
Armor affects all elements equally. Each plate reduces damage by 10%
Radiation is supposed to ignore 2.5 plates (as stated by Trick in /zone chat), but appears to not work correctly right now. This has now been fixed
Bio destroys armor plates much faster than other elements.
These numbers seemed different against another player in a duel (for example syphon had 0% vs HP), but I haven't tested that extensively.
On top of these modifiers
Radiation, electric, bio and fire weapons get a 10% card damage malus.
Syphon weapons get a 25% card damage malus.
Originally Posted by Deunan