The road back to mediocrity

As a runner I am nothing short of mediocre, I have slowly and steadily increased my speed over time and knocked an average of 10 minutes from each of my PBs for 10k, half and full marathons since beginning running (almost 4 years ago). I will never be great but I have discovered that I have good stamina if not great speed and am well positioned mentally and physically to give ultra's a good go. There is, however, a lot to be said for mediocrity and without it the truly great would not seem so great.
My first solo 12 hour race was scheduled for 3 weeks time and training was going well so imagine my frustration when nearly 7 weeks ago someone rear-ended me and I injured my back. I am now slowly getting back to running and was torn today as I returned from my run... trying not to do too much too soon I did a 3.5 mile run, on roads and into the woods but was saddened when I arrived home to see my pace had been much slower than it felt. 
This has cemented the decision that I will withdraw from the 12 hour lightning run and focus on getting back to full fitness in time for the Mont Blanc Marathon in the summer.