Anything under 30', tandem is fine as long as you have 6000 lbs axles. I have a 38' gooseneck with tandem and pulls like it isn't even back there. Of course, I wouldn't have 5200 axles on anything more than a 20' open trailer.
Beast, you're trailer seems heavy. My 38' weighs in a little of 5K. Our new Haulmark title weight is 9900. But I don't think it is that heavy. Should have weighed it before I started to load stuff into it.