I went to Diamond Marine website and looked at the trailer without your boat sitting on it. Those axles are on leaf springs and look to be mounted to a plate held on with U bolts. They can be moved forward to better balance the load. For short runs, the 8725 should be OK for your use once correctly set up. For long distance travel, I'd either go for the tri-axle or a different brand, heavier built tandem. Venture brand trailers are a lighter built trailer from what I've seen.
With Parthery's calculation, you will be over on the 8025 trailer, the 8725 would better suit your needs once it's set up correctly. Venture and Vantage are the same trailer, I reached out to them and asked. Each trailer dealer has to set the trailer up to the boat, the manufacturer ships them set on a factory setup, once on the ground, dealer is responsible for setting trailer up for the boat.