But, having no proof for either yes-existence, or no-existence, wouldn't the most honest position be that you cannot really know?
By that standard, you are not a theist.
There is no way for anyone to know to a 100% certainty that there is or is not a god. Those who profess to be atheists must acknowledge, if they are being honest, the possibility that a god does exist somewhere in the universe that we cannot know about. And, those who profess to be theists must acknowledge, if they are being honest, the possibility that the being that they believe to be god could be a complete figment of their imagination, or perhaps an alien life form that has fooled them.
Of course, this isn't what normal people mean when they talk about theism, atheism or agnosticism. They talk about belief, not 100% certain knowledge. Any reasonable person, if they give the matter a modicum of thought, understands that in matters of faith, people come to the conclusions that they do based on a level of evidence that they are comfortable with, but that level is nowhere near absolute certainty.
This distinction is one that I have seen religion pushers use to try to convince atheists that atheism is an irrational position. Since it's impossible to know everything, the argument goes, one can never be certain that there is no god. But, since by definition one can never be certain about anything in matters of faith, it's rather disingenuous to claim that a lack of complete certainty somehow undermines the legitimacy of atheism.
Those who would sacrifice an essential liberty for a temporary security will lose both, and deserve neither. -- Benjamin Franklin
We see monsters where science shows us windmills. -- Phat