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The south side of Loch Maree, once they reach the widest part, is on the A832 [so fast]. I don't know the track that climbs up from Poolewe and then drops down to the shore, but the north side of the loch is much slower going in the second half: IIRC there are some farm vehicle tracks that are likely pretty bad now and it's mostly not even that.
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Indeed there's an actual road. Looks like it's about a 20 km section of something like single track either way, but then also about the same length of the road for this year. Dotwatcher says it's Tollie path
https://www.youtube.com/watch?v=qwNAfNRRH9I
This year's route goes to the other side of Loch Maree compared to the year the record was set. That was on the east side on the orange line. So looks like there won't be a new route record this year, though I know nothing about those trails.