simcgunner,
What threw me was them being called Sika Elk in the first post. At less than 90 pounds, they are smaller than even our small Alabama Whitetail. In that case, 6.5x58R will work with a careful shot. It is about equal to 6.5x52R, which is the 25-35 loaded to slightly lower pressure. Good luck, it seems like you have everything well in hand. Be sure and post a photo for us to get jealous over.
Mike