Ted,
I've built a Northeaster and have spent some time rowing in a Light Dory (Bolger), Mollyhawk (Welsford), Flint (Lillstone), and a Gardner Gunning Dory. I'm a fairly big guy (6' 250lbs), and row in a pretty wide range of conditions ranging from flat water in the Sacramento Delta to cautious venturing into the Pacific off the Sonoma Coast.
In rough water, the big gunning dory feels safest, but windage can make it a real pig to keep on course. Even in smooth water and dead calm wind, it's not all that fast. If you push things too far and capsize, the gunning dory is very hard to right because of its weight and high freeboard.
No offense to Phil Bolger fans, but the only virtue of the Light Dory over these other boats is that it's easy to build. When you're finished you end up with a boat that's slow, tender, and has a remarkable tendency to weathercock.
The Northeaster, Mollyhawk, and Flint are all faster, track better, and run drier in rough water than the Light Dory. That said, there are two differences between the Northeaster and Mollyhawk/Flint you might want to consider:
On the minus side for the Northeaster, using a motor is difficult. Yes, a motor, which is very useful when fishing. I know, fishing from a dory, who would have thought? Also, the motor can often be a lifesaver (literally) when the weather turns bad and you are miles from shelter. I've got a jury rigged setup on the Northeaster that holds a 2-hp Honda off to one side, but it does not work nearly as well as a real transom. The Flint adopts to power exceptionally well for a boat designed primarily for rowing.
The second consideration is rowing in rough water. This is where the Northeaster wins hands down. Both the Mollyhawk and Flint can get pushed around in a following sea if you are not careful, and have a tendency to broach if the bow gets the least bit sideways to the wave. The Northeaster is well behaved under these conditions, and tracks straight.
Bottom line: If you want to row for pleasure in open water, the Northeaster is about as good as it gets.
Gary