I think we need to differenciate between "most difficult ascent" and "ascent I/we/you found most trying"
Climbs later in races will always feel worse (like those at the end of the Long Mynd race, which Wheeze rightly mentioned). Things like the Glamaig and the Kirk Fell climb will feel different because they are the only climb in a short lung-bursting race.
I can vouch for the pain involved in the Wasdale Show race - going up AND coming down!!