Hi Paul,
Like Diana, I too was part a church but not heavily involved in it. My advice would be very similar to what Kat gave, be up front and tell your church you are leaving. There is no need to tell them why, other than for personal reasons. Being from a small community myself many years ago, it matters not what they are told, for they will make their own mind up.
Personally, I would tell tham that God has opened your eyes and heart to an understanding that is in conflict with the teachings of the church. This will of course cause quite a stir, but trust me, they will not be able to prove you wrong, and neither will they be able to prove their belief. More than likely you will be told that it is not up to you to understand everything. I will leave it up to you, how you will repond to that. Speaking from experience, stating something like: "can you not with your enlightened understanding explain in such a way that I can learn" does not really work. Especially when they back down and you close with: "it's because you can't right?"
I have used this a number of times, and any further conversation promptly stopped. I guess this is the one thing I have found while in the church, NO ONE likes their faith being questioned and they will back away from you as iff you had the plauge.
It will not be pretty, but at least it will be over pretty quickly.
Trust God to give you the words and the wisdom of how to use them, and I am sure it will work better than even you imagine.
I will pray for you,
Darren