My advice would be to set off at 6:00 per km, which for you, will feel easy, but that’s the skill to marathon running. Holding back so you have enough left at the end. Is Sub 4 achievable? Possibly but also involves the risk of running out of energy at 20 miles and then really struggling. Hence why I think the slower start is better. Fuelling is something I do worry about with you so please please do take on some fuel. When I did it last year lots of people left water and food on the chicane just before the finish line, so perhaps something to consider. Best of luck Allan, you’ve trained well and I think you’re in good shape to run a great race. You got this my friend.