I don't really have firm beliefs about the nature of time, so you could say I truly am an agnostic in this regard. I'm not sure how special relativity would contradict the "sufficient conditions" (determinism) theory and didn't track your argument very well in this respect.
I think you are very right in noticing that the question is "why did we make the choice that we did." One way to answer that question is that there were sufficient conditions to cause that choice to be made, or that it resulted partly from random chance. Your "third option" is not distinct from the previous two.
If a decision is only "largely influenced" by some conditions then those conditions are not sufficient for that choice to be made. This then begs the question of "Why did the person make the choice they did?" To answer this question you can either add to the previously mentioned conditions until they become sufficient, or you can say that there were not sufficient conditions for the choice to be made. In the later case that would mean that the decision was at least partially uncaused.
A common notion is that if someone did not have acted otherwise than they did then they are not responsible for their actions. If this premise is accepted then the answer is that people are not responsible for their actions. However, it can also be argued that someone is responsible for what they cause. In this sense someone is responsible for their actions in the same sense that my car is responsible for producing exhaust. I don't really care how the word is defined as this is just arguing over semantics.
I find it a little hard to believe just about anything could happen which is not the will of a tri-omni God that created the universe. In that case we would only be acting the way God wanted us to now. The only other option I can see is that God somehow created a universe in which things just randomly occur without cause, which doesn't help the case for free will any.
Like I mentioned earlier, my position is that if you can tell me what free will is then I will tell you whether or not we have it. I don't believe "free will" is a particular property or aspect of the world that we are just seeking to discover. I think it is a vague human-invented concept that people are seeking to impose on the world. However, if one closely examines the possible ways the world can be it is discovered that none of them jive well with our intuitions about free will. Additionally, no concept of free will can be concocted that is consistent with a way that the world can be and which would shift responsibility for our actions away from God and onto us.
Consciousness is a complex thing, but not fundamentally different from other things in that its actions need causes, and there can be sufficient causes for conscious actions or not. The conscious control you speak of means primarily that we have thought about stuff during our decision making process. This would not change the determinedness of that process or the resulting decision.
It can easily be independent of any argument about God. However, that is where free will arguments tend to come up.
It is a dichotomy. There really are only the two options I've been discussing. The "3rd option" you are proposing must fall within one of those two options. Again, just what is this free will you speak of? It cannot be defined in such a way as to create a third option.
You're not alone, and there are very intelligent people who aren't. I haven't seen anyone come up with a legitimate third option though.
