I know God exists & the court of highest appeal is me.

The concluding point of my arguing so is to stalemate the objection "how do you know it is God and not Shiva". The question is as useless as the question "how do you know you are not a brain in a jar"

True. What we can all say is that "I know x - subject to my perception of reality accurately reflecting whatever the actual reality happens to be."

If both manifest the same way, the same logic applies in describing them both. Only in places where the two would of necessity be different (which, you assert, is nowhere) would this line of reasoning be in any way meaningful.

Therefore, if reality is objective and external, the interpretation of reality that is most objective and external is most likely to be correct. Well, seeing how religion relies on personal feelings and interpretations, while science relies on outside observation and repeatability, I submit that science is more objective and more external. So, here are the two options that this entire line of reasoning permits:(1) Subjective reality: We're both wrong
(2) Objective reality: You're wrong

So, the question is, either the "external reality" is the right boat, or it's the wrong boat. If it's wrong, then both theists and atheists are wrong together. If it's not wrong, at least one of us is still wrong (because, in an external, objective reality, we can't both be right).So, we're only in the same boat if we're all wrong. This doesn't drive the argument to stalemate, because it only stalemates under the condition that everybody's wrong. This effectively polarizes the argument (i.e. leaves no room for middle ground).

Both theistic and atheistic approaches depend upon some external source of reality. This, you believe, puts us in the same boat, and renders all our claims about reality utterly subjective and completely equal in validity. I can understand this logic. That boat is the "external reality" boat (as opposed to the "subjective reality" boat).

But, the stalemate only comes when everybody's wrong. If we're together in assuming an external, objective reality (even if it isn't objective or external), the one of us whose system of interpretation actually is objective and external is much more plausible (because subjectivity cannot have any bearing on an objective world).