I am using Gore trailers as examples, because they are manufactured and have a wonderful dealer near me, and all I have ever owned. Floor plans and all measurements are on this web site.
http://www.goretrailers.com/
Two horse straight load bumper pull with flat front and no DR is 13’4”.
Two horse slant load bumper pull with aerodynamic front and DR is 14”6”.
Two horse bumper pull straight load with aerodynamic front and 5’ DR is 16’6”. DR is 3’ on both sides and 5’ measuring into the nose.
So, if your goal is to have a DR and also have a trailer length as short as possible, then a slant load might be the best choice, as overall it is only 14” longer. It is a bit wider, but only by 7”. If you have just the one horse, a manufacturer could modify the divider placement to give your big horse his own big space. Or, just take out the divider, store it away for future use, and have a single horse trailer with one double-width standing space.