"PS - For that last part, I'm speaking of true Christians--if there is such a thing--who want to live by the Old Testament and New Testament simultaneous--which is inherently so contradictory to be literally impossible"
I'm one of those (loosely called "Messianic"). It is only impossible to people who don't have understanding, and never read the complete text in Hebrew and Greek. There is no contradiction in the two, once you realize that translators made grave errors in translation, and often missed the nuanced inflections in the Hebrew. I will give a simple innocuous example that really won't change how anyone views the rest, but it makes my case fairly clearly in a way that even people who don't know anything else about the Bible can understand.
The word "Sheol" is translated as "grave" or "underworld" or "dead in the grave" or any other number of ways, misses the real point, which is hidden in the root. The word "sheol" has a inflection of a interrogatory (question), rather than an absolute. It is like how a parent answers a young child's question, "Where's Grandma?" after grandma dies. The Hebrew word "Sheol" defines the answer as a question.
There is an unknown, after death, including the possibility of nihilism. This is what the Hebrew text implies, for it is an unknowable answer this side of eternity. It is a question, one we ALL must ask, and answer. Those that are 100% sure are the ones I'm fearful of, from Muslims and their 72 virgins to atheists who are 100% certain they are correct. These are the people who are dangerous, because they will do anything to defend that belief.
Sheol is the answer, that is itself a question. But how does one translate the untranslatable? "Death", "Dead in the grave", "grave" those work, but don't convey the totality of the word. Translations never can quite get the full flavor of the original language.
And before you go off on my choice in faith, please be aware that most of what you think of me is probably wrong, because I am also a political libertarian, because that is what my scriptures indicate (Law of Liberty). My G-D gives me the choice to choose. HE is not a tyrant, but HE does expect us to be accountable for our actions and choices, and intentions.