Rough figure, starting thru hikers do maybe 10-12 miles/day through GA. Average. But average is pretty meaningless... For one thing, the range is huge, exceptions all over the place, etc. My number based on casual observation.
If you've got your gear dialed in, and are in shape, etc., you can do more. Or if you want to relax, you can go as slow as you like.
There's no need to let the statistics set your goals.