4* is not very good artifacts, depending on where you are in game. Most people would recommend NOT taking them to 16. Wait till you have at least 5* artifacts/accessories. You will definatly end up selling 4* at some point and it cost you a lot to get it to 16.
Speed doesn't add much power, Resistance does. It doesn't make resistance better, just the way the different stats are counted. You could stack resistance on kael and get a lot of power. But who cares? What good does it do him? He's a glass cannon. Make him hit hard and fast and he'll be a better champ, with less power than some others.
Do you have you Kael booked?
Do you have masteries on your Kael?