It's all about how much money you want to spend on pumping your well water. Deeper isn't always more important. If your serious goal is to have year round trout, I would keep it right around 6' deep, but keep the banks of your pond steep. Minimal shallow water areas will help limit solar heating of your pond. See what the temp of your well water is. Realize the bigger the pond, the more well water you will need to pump in it to keep the temps down in those toasty warm summer days. Shade would help some, but again the biggest factor will be pumping large volumes of cold well water into your pond. You will also need to aerate that well water to increase the DO in it as well before it goes into the pond. Ask Cecil Baird for his advice, he has done what you are trying to do and can provide far more advice.
