An interesting thing about the newer diesels is that it seems that trailer size doesn't make much difference.
I can put my tandem utility trailer with a Kubota tractor at 6000 lbs behind me, or I can more than double that weight with my fifth wheel (which is like pulling a parachute) and I get 11.5-12 mpg with either one.
I doubt you will ever justify the diesel based on fuel mileage, even though the diesel will get almost twice the mpg, unless....you intend to drive them for several hundred thousand miles...even then, with the additional maintenance cost...
Were it based purely on the numbers, I probably would have saved the $8500 and bought the gas engine. But, whether I'm driving solo, or towing 13,000 lbs of trailer, the diesel doesn't seem to labor at all, and the dang thing will still accelerate going uphill while moving 22,000 lbs. I guess I still have a little testosterone left, because that's hard to not enjoy.
But I'm afraid you're going to be hard pressed to justify the diesel for a 10,000 lb load.
2016 Ford F-350 Lariat CC, 4x4 SRW. B&W turnover with extender. 2015 CC Silverback 29RE, fitted with Reese Goose Box. Amateur Extra Class K5TS, 2016 nights camped 16