Congratulations on qualifying for Boston. I found "Jack Daniel's Running Formula" an invaluable resource in learning how to obtain the best performance from your body. His V-Dot fitness estimator can predict your marathon time (with optimal training) from your 5k race performance. I also had a goal to run a 3 hour marathon, but my 5k race time was just a few seconds too slow to extrapolate a 3 hour marathon. I did hit my predicted marathon performance (3:06), so I was able to give up the 3 hour goal with no regret. I recognized that it might not be realistic to improve my leg speed and 5k times at age 40, having over 6 years of good training, coaching, and racing experience under my belt.
Thanks. Sorry to hear you've written off sub-3. I've got that book and many others. :-) I got myself from a first marathon of 4:22 to a 3:36 with Pfitzinger and stubbornness, to a 3:22 with Crossfit, improved running form, and more training, and to a 3:12 BQ and then 3:07 PR with better training. I respond well to mileage, but need the strength training so I can put in higher mileage without injury. Knocking off another 7 minutes, especially in my late 40s now, will probably take some coaching help.
I don't know how much credence to give to VDOT or any of the other calculators working from 5K or 10K estimates. I think they are okay for guidelines but wouldn't use one to say I can't unless it was way out of range. I much prefer a half-marathon and fast-finish long runs for predictors. I do like to run Yasso 800s for confidence though.
I agree that longer runs are better predictors than 5k's. I was limited to about 45 miles over 4 days per week to avoid injury, so you may be in a better position. The marathon is a multidimensional challenge, so there are lots of levers to play with. Good luck.
I’m not sure if you tried it, but I credit mostly strengthening my hips and core with squats and deadlifts to allow me to increase my mileage. I used to injure my Achilles over 45 mpw before strength training. After strength training I was able to average over 60 mpw with peak weeks in the 90s without trouble. In 2016 I managed 16 marathons including two PRS, a few ultras, and 3300 miles for the year. I was running doubles 3-5 days/week. Just something to consider.
I was fortunate to be able to spend about 7 hours a week on physical exercise when I was racing. My family was very accommodating for this, but my modest physical talents did not justify any more investment. I never felt the pull for Ultras or other endurance events. At 62, I think I still maintain the benefits of fitness with moderate varied exercise, with no training or racing calendar ruling my life. I've been able to scratch several other deep long term itches after I stopped racing.
