Well the longest distance I've done in a single flight is small beer compared to some others here. It was a few years ago now flying a C-182RG back from Le Mans to Wycombe which is a bit over 200 nm. At the time it was the longest distance (>200nm), longest duration (>2hr), and highest (FL075) that I'd flown.
I've done a longer duration flight since then, making up hours for my licence revalidation, but that started and finished at Wycombe. It wouldn't have been so long if I hadn't been told that the 1hr flight with the instructor DIDN'T count as part of the 12 hours
Brooklands