I wouldn't concern yourself if whether or not someone trailered a "265". Just reference the weight - after all, for the most part, weight is weight is weight.
Is the 10,500 after doing the math?
Looks like you can cheat a little bit, as well, if that is a far as you're going to trailer.
Do you NEED to get rid of the 25-year old? Can you keep it and get a different vehicle for daily driving?
I've towed with both Sub's and Exp's. Much more so with Sub's. I used to have a boat that weighed in right around 10K and I towed that with a '98 3/4 ton Suburban. Never had an issue with stability, breaking, etc, etc. I towed very regularly, sometimes over 500 miles at a shot.