You did pick up on one of my concerns - cold water! So late June makes sense. That also gives me a few weeks down in the Bay to prep and do a bit of local cruising.
One of the primary reasons we'd head for Cape Cod in August, was to swim. I've never been much for swimming off the boat since moving to Maine nearly 20 years.
Things have changed a bit. For the last several years, the water in Penobscot Bay has been warmer(I know if anything, my tolerance for cold water swimming, has decreased.
In my area (Western Penobscot Bay), mid summer has water temps in the 60's. I keep a thermometer onboard. I'll consider going in when it reaches the high 60's.
Fact is, we've been finding low 70's occasionally in coves and anchorages not far from open water(up estuaries, even warmer).
The Gulf of Maine is one of the fastest warming sea bodies on Earth.
When the air get's into the 80's (and it does get into the 80's on the water in August-90's not unheard of), we've been swimming off the boat. I can hardly believe this myself.
But we still have the cool nights on the water.