Nice. I'd try to integrate the knot into the bow, makes a nice feature.
On the outside half I'd get down to 1 ring above the back and then check. You need 1 1/2" x 1 1/2" minimum at the bow's center. But bear in mind at 68" long you can adjust, making best of what width you have on each side. Like John says, better to slight one and get a sure thing, than to slight both and get two littles. Depending upon how the grain runs I like to bandsaw but you need to get the belly worked down perfectly so the stave rides the table keeping the blade perpendicular. If you don't you'll be fat on one side and narrow on the other.
This is what I mean by incorporating the knot. Not the knot itself, just the shape of the surrounding wood.