the ever shifting stable loaded with comfortable road bikes and city and winter bikes
I think its a pressure/ contact patch issue....how high is the pressure for the 35 mm slicks?
I don't use Shwalbes, I'm a Conti rider, but have been switching around on a few fat Conti semitread and slicks, and my take on them is pressure matters.
I went with 37mm Travel contacts because they are rated up to 100PSI in that width, kind of rare. They're semi slicks, but roll real fast because of combination of high pressure and large contact patch.
The 37mm 100PSI Travel Contacts are definetly faster than a 37mm wide 70 PSI Conti Top Touring (which i think is a rough equivalent to the Marathons?)
I think the Travel Contacts are even faster than the 37mm Sport Contact slicks I've got that are rated 85 PSI.
On Friday I pulled in a serious roadie on my LHT with the Travel Contacts, and as he caught up several miles later, said, "it's real hard to pull you in" which to me was partially an indication of the speed of the tires, as I'd already ridden 40 miles on a bike 10 pounds heavier than his.
There are a lot of different Marathons, do your have the slick treads? I have some that are slicks all except a very fine series of depressions, but there is another marathon that has a tread.
Slicks mater, size maters, and pressure maters, and they all mater to a degree where you can tell the difference. I'm no rondoneur guy so I have no idea what you should use, but my touring range loaded is 32mm to 38mm. So I would wonder why for any unloaded riding you wouldn't be running, say 28s? The move to 35 seems a little conservative, but I don't do what you do...