I don’t recall a pre-tubeless Ksyrium Elite Disc wheelset and so don’t know the exact specs, but I don’t think Ksyriums were ever aero, certainly not like a modern carbon fiber wheelset. Based on my own experience with Ksyriums (I still have a set), aero rims, and CF aero rims, I think a pair of carbon aero wheels would be real game-changers.
The benefits of a wider rim were mentioned, but I think the benefits of the aero effect are being under-appreciated. Sure, wind can present handling problems at some angles, but at others, it can really sail a deep-section wheel. Regardless of that, though, there’s a big efficiency difference between a non-aero wheelset like Ksyrium Elite and a well-tuned aero wheelset.
i haven’t directly compared my Ksyriums to my 45mm carbon wheels, but I’ve not ridden the Ks in years because my 30mm deep, aero alu wheely GB were so much better. Without even trying, my 45mm CF aero wheels put my solo rides today within spitting distance of some of my PRs set on group rides back in ‘15, so there’s some real effect going on. Unfortunately, I’m also nearly 20lbs heavier, so the wheels ain’t fixin’ that!
Additionally, a well-chosen aero wheelset can deliver those bennies as well as substantial weight-savings over the Ksyriums, so it’s an actual win/win. For example, the rather blunt, 22mm rim height, ‘18 Mavic KED wheelset was 1670g according to Mavic, whereas something like the new Lún Hyper R45 with aero optimized, differentiated F/R rim depth and profiles, clocks in at 1322g, saving a significant 350g, or more than 3/4lbs, which would be welcome on any Everesting attempt, I’d think.
Faster and lighter is a deal which works for me, and I rarely spend long hours in the saddle or do centuries, and as noted upthread, the aero benefits get bigger the longer one rides, so for an Everest-ambitious century rider, that should make light n’ aero even more attractive.