I don't know the conditions in your part of georgia, but with a well that makes 85 GPM you don't really need to set your pump very deep. If we had a typical 380 ft well here the water level in the well would be about 60-80 ft and we would set the pump anywhere from 120-200 ft. With a screened well the closer to the bottom the better the chances of pulling in mud. I would never set the pump as deep as you requested unless I had to.
The driller really cannot set the depth of the well, it is determined by the aquifer depth. If you've got a good strata at 380 then that's where you set. I don't know what can be done about muddy water, maybe the well could be developed further. I would get another well co. out and ask their opinion.