cdw wrote:
So, to begin, I would use the 5K predictor to marathon and add 10-30 seconds per mile. Be conservative. Running a long marathon-paced run too fast killed one of my marathon attempts. Alternatively, you could just take your long run pace and subtract 10-15 seconds per mile. Do it once and see how it makes you feel in the context of all your training. If you can't get out of bed the next morning--too fast. If you feel fine the next day, take 5 seconds per mile off each week
There’s a lot I like about your post but are you sure about this math? This would indicated you do long runs a maximum of 45 seconds per mile slower than 5k race pace. That might only make sense if your 5k time was more than an hour.
"FTP is a bit 2015, don't you think?" - Gustav Iden