I'm not saying that you shouldn't go after 2:50 but this is a bit of a tough one. I love the mileage and long runs but there isn't a ton of variety in the training you outlined. It looks like you run more/less the same pace every day and probably spend a ton of time in the grey zone (no true easy runs where the HR is significantly lower than other days, always adding on a little fatigue). Can understand something like a calf problem flaring up. Without pace work at 6-flat & under, I don't think 2:40s are possible at this point. You certainly have the foundation to chase an OTQ in your next marathon build. I would expect your race pace to be the same as your long runs. It is normal to feel lethargic towards the end of a build. I would treat the race the same as you've been treating your long runs and open a little slower than 6:30, before locking in. It's ok to run 6:45-7:00 for the 1st 5k or 10k and then settle into 6:30s. A first half in 1:25-27 would be fine as long as the weather looks good. I think you should run sub-3 no matter what. Get the super shoes. Try them out for a short run or two. Dial in a good nutrition plan. The marathon is an eating game.