This could be in infinite discussion because so much of this question is undefined.
- What is meant by "harder" ?
- Are we talking finishing a marathon or racing it ?
- What type of marathon ? Trail like Jay Peak Marathon "Jay Challenge" or Colorado's Pike's Peak marathon ? Or a typical typical road race course like Vermont City or Boston ?
-What is a Presi Traverse ? I assume this means walk the entire ridge and hit every peak from Jackson at Crawford notch to Madison in one day.
I have never done a full Presi Traverse, so I do not know if I am qualified to answer, but I have done extensive hiking over the years. I once did an over night trip where we climbed the jewell Trail to Washington and then climbed Monroe and slept near the hut on the snow, then hiked out to Crawford notch. I would not consider that in my top 10 hardest hikes. Those would all be miserable heard paths in the Adirondacks on stinky hot summer days. Seward Range, Allen and Couchsacraga/Santanoni range come to mind. Lots of sweat, very little views/rewards. Seward has a big pile of unburied human crap just a few feet from the summit canister for good measure. It was that kind of day.
I would also say my 3 attempts (with RMI) on Rainier have been very difficult too, but mainly due to my failure to do proper heat management. I turned twice due to cold at 11K feet. The 3rd attempt the entire group turned at the Crater Rim due to high winds and poor visability (the Crater Rim is considered by many to be the summit, but unfortuneately not me, so I am going back again this summer, this time via a different route). We were in a Lenticular cloud.
Last fall I went to Nepal to attempt 6000 meter peaks, but failed in these attempts because my body does not handle altitude well, I have a hard limit around 5300meters where I fall to pieces energy wise.
I have run 18 road marathons. Finishing them is not especially difficult for me. Hitting my goal pace ("Boston Qualifier") has been impossible for me to date.
Tomorrow is the Mount Washington Road race on the auto road. So far I have kept my running out of the mountains, but I may be curious to try this someday(not this year). I hear it is at least as difficult as a half marathon, even though it is "only 7.x miles". They say there is only one hill to worry about though. I wonder how that would compare with a relatively flat road marathon?
So racing a marathon at an agressive goal pace for me is much more difficult then day long hiking IMHO, as far as pure aerobic fitness goes. It takes me 3-4 weeks to fully recover. But hiking in exposed mountains presents many challenges that do not exist in controlled, supervised road races. Certainly self sufficiency is crucial in the back country mountains where as there are aid stations every 2 miles in most road races.
And high altitude (> 5000 meters for me) presents problems I do not know how to prepare for.
This is difficult to even net out, too many variables.
Interesting to compare though.
Cheers-
John