We have a Sunseeker 2300 and pull a Jeep Wrangler with no problem. We tow it with all four wheels down and have the E350 chasis...which we found has plenty of power to pull the jeep. I can't speak for the larger Sunseekers, but as for the smaller 2300 it pulls great.
What chassis do you have? If your towing 4 wheels down the E450 with the V-10 will have plenty of power. We pull a 5500 pound enclosed trailer behind our 2890. I get the same gas mileage with or without the trailer. If your putting it on a trailer you may want to crunch numbers. I wouldn't be concerned about it (personal opinion) but you will probably be right at or possibly over your limit per what the stickers say.