I have often said to keep the trailer GVWR within the tow rating for best results. Generally this is directed toward people that are new at RV trailering. Either way sounds like you are maxing out the towing and weight capacity. I think you have the experience to know how your vehicle will perform. Assuming you are patient about going slower when conditions dictate I think you will be fine.
Yes it is the actual weight that matters. However your description includes UVW that might not be accurate. Only way to really know is to get all of it on the scale and by then the deal is done. Not many dealers will hook you up for a test drive to the scale.
Legally you can tow well over the rating on most consumer vehicles. Legally the DOT rating is by axles and tire width. Vehicle rating is more about performance, warranty and what the manufacturer considers safe.
