@Judal:
Anyone else gets the feeling that Gowther might be an exiled member of the God clan? Since Meliodas is already the token pervert, I guess Lust in Gowther's case refers to thirst for power.
I believe that Gowther sin is Lust because in his past he did something based in lust and that made him loose all the sense of lust! He is an emotionless man, basically a man without emotions, without desires, without lust!
Don't forget that more important than characterizations of the actual selfs their sins are related with some regret and big offense that they made and now they are trying to forget or live with it.
Meliodas destroyed is all country because of his wrath(when he is in that state he can't control himself) and right now he tries to be all goody and funny, but he still sometimes have some explosions of anger(Like when Ban tried to touch his sword).
King was so lazy that he even run away of responsibilities and left his sister to do them, even when it wasn't her to do it. Right now he is still lazy as fuck(seen by his body being so weak and his pillow) but he now tries to be more active.
Ban was a thief motherfucker that stole everything, but then fell in love with King sister and tried to repent, but she died and he kept doing it. Right know sometimes his greed surfaces, but he does a lot of things for others, like following Meliodas.
Diane left his tribe, we don't know the real reason yet, but probably related with envy(didn't she envied the small humans?). Right now the only thing about envy that surfaces his the envy of meliodas being with other women.
Gowther we don't really know what happened in the past of him, but right now we know that he is emontionless, in speech, in motivation and in everything. That is the inverse of lust, that is the apex of emotion.