The problem of evil revisited.

[Angrboda]

character, n.
9. a. The sum of the moral and mental qualities which distinguish an individual or a people, viewed as a homogeneous whole; a person's or group's individuality deriving from environment, culture, experience, etc.; mental or moral constitution, personality.

It would seem a truism that a person of good character expresses that good character through good deeds, for what is character but the expression of such. However, I think you have a problem here in that causing a person suffering is a pre-requisite for good results, your so-called eternal reward. Thus, a person who causes others suffering is effectively doing God's work, encouraging the good result of building character through their evil acts. You've essentially defined causing suffering as a kind of moral good, which leads to the awkward result that the bully and the sociopath are actually doing good deeds, and, that thereby, they are considered to have good character and to merit eternal reward. This seems the unfortunate result you have any time you make evil a necessary pre-requisite of the good; you've inverted the value of that evil and made it into a good. You could get around this through Divine Command Theory, that the good is what God says is good, but as a deist, that route is closed to you. Thus you are left with this unfortunate side effect of sanctioning evil in order to justify the existence of suffering.