1.) Agreed, Northern New England can hold way more than 8ft, it gets huge up there. So can the Outer Banks.
2.) I don't consider Florida the Southeast, Florida is much more consistent than the southeast, swell window/exposure from both directions +exposure to tropical activity would explain that. However it still lacks the max size and power of the northeast.
3.) The continental shelf (south of the outer banks) has 2 levels, the primary one right off shore (shallow one), and the secondary one out further to sea which is deeper. From what I've read, it's the top level one that has the main impact on decreasing wave power, and the lower one is so deep the effects are very minimal. I can also sort of tell from living in several places on the east coast. East Florida gets pretty good waves and doesn't seem to be effected by it too much. (You can tell by looking at Reef Road Florida and the size it can produce) The shelf narrows as you go south in FL.
4.) Really just talking about power and size of the waves, consistency and swell exposure aside.
The older I get, the more and more I prefer consistency over size. For the kind of waves that I believe any East Coaster is used to surfing, it gets pretty consistent here in my little slice of heave in Northeast FL. We do not really get blocked from anything other than the Cape when there's a straight north swell. And even with that said, most of the time, the West-East jet stream during the winter passes either above or below where OBX sticks out so we still end up getting some.
If you've ever surfed the out islands in the Bahamas, you can tell right away there is lots more power since there is no continental shelf. Reef Road does hold very big waves ( over 15-20 foot faces ) on those rare days, due to a trench combined with the shipping channel at the inlet, plus the proximity to the Gulfstream current and the extreme eastern lie of the break. But it is not nearly as powerful as waves half that size in the Pacific, or even the OBX. This is due to the continental shelf. I've surfed Rye on the Rocks in NH, that has more power at 8 feet than Reef Road does at 12 feet ( faces). There are a few places that hold well overhead surf in East Florida - check out Monster Hole, or RCs on big hurricane swells.
Not to mention the NE has extremely varied coastline geography. Look at Ruggle's in Rhode Island. You just don't see coastline like that in the Southeat/Mid-Atlantic. There are few good point breaks south of the Mason Dixon.
First warning sign of surf that is bigger than you think is the "time warp effect" my own term for the phenomena. If the surf looks like its moving really slow from the shore, the surf is much bigger and much further out than you think. Of course most of the time on the east coast if it looks mushy it probably is, lol.