Interesting, isn't it, how we are driven toward certain questions, whether we're dealing with the Ten Commandments, the Beatitudes, or the body of the Sermon on the Mount? At least three resurface in your post: the matter of feelings, Jesus' creative use of existing themes in the Judaism of his time, and the light and dark sides of God.
Let's start with feelings. As I've noted at other times, I deeply appreciate the possible distinction between how we feel and how we act. We can choose to act lovingly toward enemies, regardless of our feelings. Doing so, though, still requires that we recognize and confront our feelings and judge hatred (and its kin)wanting. Over the long haul, I'm not convinced we can maintain a separation between feelings and actions. Jesus, in my opinion,recognized this reality. In "good Jewish fashion," he began with actions, but it seems clear from the tone and content of the Sermon of the Mount that he also dared hope feelings could be transformed as well.
Both of us probably could provide (or find)testimonies from those who have experienced such transformation. To my mind, such accounts matter. They strongly suggest our feelings can change, or be changed. Jesus' vision moves beyond the question of controlling our feelings. He seems to call us to yearn for new and better ones. This particular topic gets caught up in the larger Christian dream of a life made new by God.
As to Jesus' creative use of Jewish themes, I think we are in full agreement. The very idea makes some Christians uncomfortable. A few probably harbor a bit of antisemitism. Most, though, are guilty only of muddled thinking, the kind that insists Jesus's perspective and teachings must stand alone, divorced from historical setting or precedent. Such thinking ignores the implications of the Incarnation, to put it gently.
The light and dark sides of God--now there's a matter that has deep roots in Jewish history and interesting outbreaks in Christianity's story. We've played with Yetzer haTov and Yetzer haRah in previous posts. Christian scholars began to wrestle with the topic as they became better acquainted with rabbinic writings. Some Christians speak in terms how light must always cast a shadow. Personally, I think the concept lies in back of the Apostle Paul's confession that he does not always do what he wills to do, not to mention his insistance that the "fleshly person" must die that the "spiritual person" might live.
We may be close to a functional agreement on what to do with our two natures. You write, "Maybe we can understand Jesus' command to be perfect to be a call to recognize our dual nature and place rah in the service of tov, just as God softens His judgment with His compassion." From my perspective, rah and tov both must die in favor of a "resurrected" and unified self, characterized by grace and strength and genuine wisdom, by a new life devoted to the worship and service of God.
These, of course, are deep matters. I am not certain I've yet found the language to express them well. Ah, yes...that's one of the purposes behind our conversation!