If it were me I would pull the pump and everything out and then blow the well with air. That will tell you the exact GPM the well is making. I don't know what you're trying to do as far as household, irrigation, etc, but 10" well is a pretty big well round these parts. Also the condition of the original well plays into it. If the original well is steel casing it will eventually get a hole in the casing, if not already, and you will have to drill a new well regardless. Sometimes you can acidize the screen, if it has one, to increase production. This is not done much anymore on steel wells due to most of them already having a hole in the casing or the fact that the well is nearing the end of it's lifetime.
If the well only makes 2-3 GPM it will be a chore trying to keep the pump from running dry. You will have to install something like a pumptec etc. to shut the pump off. Also I would go down to a 1/2 HP pump. Remember too that when you're pumping open ended you're pumping much more water than the pump can do at 50 psi.
There is approx. .6 gallons of water per foot of 4" casing, so you should have several tens of gallons of storage in the well. I didn't see what your static level was but I have a well that is a low producer but the water level is about 20' with a total depth of about 220, giving me about 120 gallons in storage + the recovery rate of about 5-6 gpm.
That extra 17 ft gave you about 10 gallons more of storage, so your extra minute sounds about right.
Good luck to you and let us know how it turns out.