When I finished, I had beaten Eric's time. But did I beat his ride?
I am fully aware that I covered a shorter course than he did - possibly as much as 9 miles less. If he covered 849 miles in 54-18-35, then his average speed was 15.63 mph. My ride certainly benefitted from the Dornoch Bridge, which lopped 7 miles off - maybe there were other shortenings. If my distance was 840 miles, then my speed turns out to be 15.71 mph.
So does that exonerate me from feelings of guilt? I'm not sure, because the difference was not just miles. The new route allows the rider to replace a 34 mile segment with a totally different 27 miles, which loses a large climb (the Struie). On the face of it, therefore, I had it easy. However, I contend that I found the (flat) road to Tain quite boring, and concentrating was a problem. On the day, I could probably have coped with the hill.
There remains though, obviously, the unarguable fact that I took the short route. Any course changes will inevitably blur comparability between rides and riders, and so there can always be questions of who did the best rides.
Having considered the difference in course, the question then becomes whether that is the only factor which affected the rides? Of course it isn't.
The End-to-End is a contest between riders and a vast array of obstructions. Some, like the chosen course, are known in advance. Others are partly known, like the weather and the rider's fitness. Others are totally unknown, such as how the rider will cope with missing sleep, and whether mechanical problems will occur.
In the end, the bottom line is that the person holding the record is the one who got from place to place in the shortest time. There will always be differences in rides, and so there will always be subjectivity in comparing performances. Taking any high-level analysis to extremes, the best rides were probably done in the late 1890s!