In Podcast 57 Dave Troman and I (john Kynaston) discussed whether to ‘race’ the Fling in preparation for running the West Highland Way Race or to treat the Fling as a good long training run. People have different ideas and obviously there is no ‘right’ answer.
One of the other things we discussed was whether you can predict your West Highland Way time from your Fling. I decided to look at the times from last years 2013 race and see how it worked out.
411 people completed the 2013 Highland Fling and 149 finished the 2013 West Highland Way Race. Of those 149 finishers 81 ran both the Fling and West Highland Way Race.
I divided the West Highland Way Race time by their Fling time to produce a factor and then averaged them all. The factor came out as 2.19.
So all things being equal if you multiply your Fling time by 2.19 then it will give you an idea of your time.
I have run the West Highland Way Race 6 times. Each time I ran the Fling in preparation. So here are my stats.
The first column is the year, the second column are my Fling times, the third column my Fling time multiplied by 2.19 to predict West Highland Way time and the fourth column is my actual times. 
So for most of my West Highland Way races I did better in the full race than my Fling time suggested based on the average.
Anyway food for thought!!
Spreadsheet comparing Fling and West Highland Way Race times in 2013