Those were shoreline mounted speed gun acquisitions if I recall. I'd venture to say that less skilled skiers running -22/-28 can do so with lesser "speeds" than displayed by Wade Cox; that is he's skiing his longer lines in "prep" for shorter. At some point the critical path as the line shortens (-38) requires greater velocity. It'd be interesting to see speed gun data at -39/-41, as well as the location of max speed (center-line, off 2nd wake, etc.).
One can snapshot "speed" and try to surmise differences at -38 and shorter, but speed is merely a scalar quantity and doesn't reflect the real challenge; adequate velocity or momentum (MV - conceptualize the vector quantity). IMO this topic is what GUT centers upon; getting "up on the boat", not just trying to ski "wide".
Running -32 and sometimes -35 can be hacked through by "taking the handle where I want it to go", but with poor momentum and end up chasing the boat. If -38 ever drops it'll require re-training the mindset to ski by "following the only path the handle can go"; with improved momentum; carrying me "up on the boat".
So it's not necessarily an apprehension of "speed" but rather, a lack of concept (or ability :neutral:), but it's remediable.
There's a lot more to it of course but thinking about it on the ski is fruitless imo, just gotta do it.