I didn't have to race a lot to know what I could do. My workouts were telling me. .
This is how I felt in my buildup for my last marathon. It wasn't that I was plugging workout times into a calculator to see what I could do in a race, but I could tell how things were going by how the workouts felt, relative to their pace and the overall training load.
When I put my recent marathon time into the calculator on this site the training paces were kind of close… The faster stuff was almost right on, but I seem to run my easy days a bit slower. Safely getting the volume in was more important than hitting a predetermined pace; and being fresh for the hard days.
It's always good to have a long range goal to look ahead to, but don't forget your primary goal Ed, just getting out there every day. I know for certain that the one thing that made a huge difference in my training this last cyle was running every day, and bumping my mileage up from around 50mpw to 80mpw. Get there healthy, hold it for a few months, and you will have positioned yourself to run faster than you ever have before.
Do or do not, there is no try.