Which model are you looking at? I have a '94 244 which has the notched transom. It has the original Yamaha 225 (TXRS) and a 9'9 Yamaha kicker. I have taken it to Tantas Ledge and the north end of Jeffrey's ledge in the Gulf of Maine, but I only do it on the "right" day for me which is light/variable winds and nothing more than 4 foot seas in the forecast, mostly because I have my kids with me, but I also don't want to get pounded too bad. I spend most of my time in Saco Bay. I can tell you my boat handles these conditions well, with little to no spray in the cockpit. It impreses me, but then I'm easily impresed after spending most of my previous time in a 17' bowrider.
As far as +/-, I think the biggest plus is the big cockpit-plenty of room for fishing. If you've run Grady's already, you know about the other plusses when it comes to fishing setup. Some people don't like the idea of a notched transom, but I have never had a problem with water coming in from a following sea. MAKE SURE that you have the transom checked where the aluminum trim covers the top of the transom. I removed mine and there was NO sealant in the gap between the liner and the hull! Luckily I caught it before it was an issue. I can't believe it came out of the factory like that.
I can't speak for the Gulfstream or Seafarer, never been on one, but there are lots of threads that talk to the performance of both. I think there were also I/O and bracket drive models as well as twin outboards for the Explorer, but I haven't been on one of those either.
Hope this answers some of your questions.