Hi . I guess I’m going to be on the other side of this discussion… I wouldn’t go for the 8’ . I would go 7’ the reasons are a few 1 once you fill that unit to full capacity you are going to know it’s back there … 2 Not to condone your tractor you have to remember that you are on rubber… regardless of the weight of your tractor you’re still going to have some issues pulling it. I base these comments on I’ve run a few scraper pans front and rear powered and once you try to load and pull it’s tough going unless you’re being pushed by a push cat. I also have owned a 2014 5115 m loaded like yours almost to the t . Except the tires .. I was not impressed with it as far as it being a tractor period! I sold it and don’t regret it . They are not all the tractor that Deere thinks they are. Please don’t change your opinion because of mine… I’ve just been around Deere and they think they are the best …. I got a bad taste in my mouth from. Good luck with your decision.