From another forum where I answered this with:
Alasdair, the higher operating pressure, the more water you use and waste is greater. I suggest 30/50, it is the norm.
Your 99' - 10 to set the pump at 10' off the bottom = 89'-12' static level =77' of water and a 6" well gives you 1.47 gal/ft = 113 gallons of water with the 6 gpm recovery rate. I would size the pump to pump from a water level of 90' and give you more than 10 gpm.
I sell water treatment equipment and it all has to be sized for the peak demand of the house as to how the family uses water in the number of bathrooms AND the type of fixtures in them. I sell for houses that have a 20 gpm shower alone! Large tubs can flow at 9-12 gpm, alone. So I do not agree with 10 gpm peak unless you do not have any large tubs or two person or body spray showers and won't in the future. My equipment records the highest gpm run through it each of the last 7 days and then, the highest gpm ever run through it; I've not been told I have been wrong on their peak demand yet, out of 1200 sales of that control valve.
Without looking it up, I'd suggest a 230 vac 15 gpm 1/2 hp submersible set at 89' on 160 psi rated 1" PE pipe and a dovetail type pitless adapter and the same PE pipe to the pressure tank.
You do not need a large tank, and thinking about it, you can't use a large tank to make up for a low producing well. Every drop of water used is then taken from the well all at once to refill the tank. And at 40/60 your draw down of the tank happens quicker so the pump runs more frequently and often. What 'extra' water do you get from the well?
I suggest a small tank and a CSV (Cycle Stop Valve) which provides constant pressure and doesn't refill the tank until you stop using water.
Do not buy a pump or tank from a big box store, they are low quality, a pump guy will have much better quality.
