Personally from what I know, I would opt to get the 10k trailer. It's better to error on the heavy side on trailers than too light. Always room for growth. Just like most people wish they had a bigger more powerful tractor rather than a smaller one. :laughing: A F-150 can still manage a 10K trailer depending on terrain, engine, trailer brakes, etc.
I currently have a 16ft P&T trailer that has two 3500 lb axles. Most people forget to subtract the trailer weight from the gross rating. My trailer weighs 1600 pounds empty. So to be safe I can only carry 5400 lbs. When I bought the trailer, I didn't plan on getting a tractor so soon; therefore I feel I am close to being "under-trailered."
I ended up getting a Mahindra 2816 with a FEL, backhoe, and rear loaded tires. I am well up into the 4K range. The 2816 stripped is 2305 pounds, FEL weighs in around ~750, and the backhoe is 1250 pounds. I am not sure what the loaded tires weigh, but I would say a couple hunderd pounds a piece. My trailer handles the Mahindra well and I don't see any signs of stress, but sometimes the trailer will flex slightly.
I will say that 16ft trailer with my backhoe attached is too short. I would opt for the 18 foot trailer if I was doing this again or were in your shoes. My buddy just bought a new
L3800, so I know the tractor you are talking about. With the FEL attached it is much longer than my Mahindra.
In any case I would definitely recommend trailer brakes. It will save your truck brakes, not to mention your sanity when going down steep grades.