First off, the static height of the water is as important a factor as the depth of the pump. It determines both the storage capacity and the height the pump needs to lift. The storage capacity determines how many gallons you can pull before the well's recovery rate becomes an issue.
When my mud well was put in, the well driller left his 5 GPM running for days, both to get it to run clear, and to satisfy the mortgage lender that there was adequate GPM of recovery. When I put my 10 GPM pump in the well, it immediately turned muddy and actually sucked mud up into the pump.
Now, I assume at 240 feet that your well is drilled in rock and that eventually it will run clear. A 12 GPM pump with no pressure (depending on the size of the wellhead faucet) could pump more than 12 GPM but if you are pumping the well dry, that is eventually a column of 240 feet of water the pump needs to lift. With every 2.31 feet equal to 1 PSI, that's around 100 PSI down at the pump. Surely that should regulate the GPM down to something the well can recover from. Did the driller's report state the GPM the well is capable of?