Wow! beautiful site. I miss New England as I used to live a stone's throw from the New Hampshire line in Massachusetts. I have fond memories of catching brookies in a spring fed lake near my house.
That said, as one who is raising brook trout right now I would not give up on trout either. 60 gpms of flow is more than enough to keep trout if you manage it right. However you may want to attempt to divert runoff from summer thunderstorms in the future if you go the trout route again.
I have an 88 by 59 by 9 foot deep pond on my property that I have grown brook trout over 5 lbs. with only 38 gpm. The pond is about 117,000 gallons.
The trick with trout as you probably know is you must keep water temps between 55 and 65 (most of the time but you can go a little higher if D.O. levels remain high) with at least 6 ppm of oxygen. If you can do that you are home free. From my limited experience I have found you should have a pond that has a low surface area for depth to keep temps cool but I also use a 1/10th hp compessor/diffuser system to keep the water circulated. However I heavily feed my fish and removed over 500 pounds of trout from this pond this fall. If you do not stock heavily, do not feed, and have water that has a low surface area ration to depth you should be fine w/o artificial aeration. However it would be a good idea to do some form of natural aeration as in a fall or something just like they do in stream improvement. I would think you should be able to have a pond up to a half an acre with 60 gpms if you do everything right or even better would be again a series of smaller onds as you had before
Obviously your original three ponds did not warm up as readily as the one larger pond. And correct me if I am wrong but I believe you had a drought recently which may have contributed to the problem.
If it was me I would go with the trout in a hearbeat and I do understand your leaning to the pumpkinseeds if need be as they are a cooler water fish than bluegill and probably are easier to obtain in your area.
