I keep hearing what I consider the somewhat the misleading information that one misses out on great Chesapeake sailing with more than 6' of draft but having cruised the Chesapeake with 6'4 - 6'6 draft current boat for the past five years I see almost no difference in where I can go between my current boat and the 5' draft boat that I had before her. For many years I cruised with a boat that drew over 7 feet and they seemed to go wherever I went with my 5 feet, just more carefully. I would think that you needed to get down to less than 4 feet to see much of a difference in cruising grounds.
The thing about deeper draft fins vs shoal draft or wing keels is that the shallower boats have a lot more drag. The difference in speed doesn't show up much in higher breezes, and so the relatively small rating difference, but in the Chesapeake with our predominantly light winds, it makes a huge difference in the number of sailing days per year that you will actually get to sail vs motor.