Given your past skill level, my bet is the holders. They will be mounted slightly differently from the center line than your 4ks, the feeling of no edge is when you are balanced more over the top of skate blade (skate blade is more vertical to the ice hence less grip), the 4ks may have the holder mounted slightly to the outside of the center line and this gives you a feeling of more bite as you tend to pronate slightly into the edge when they are mounted like this. Add a different profile into the mix, or at least a new 10' in the 100k's, and there is now a lot of changes between the skates.
This holder mounting difference is really common, we did a test where I skated unlaced with a bunch of Jetspeeds and 1S skates and I could when tell the holder was mounted on a different center line, every skate was different but laced up I could hardly tell the difference). 1mm makes a hell of a lot of difference yet this is within accepted tolerances by the manufacturers.
So without ripping off the holders to get them remounted, I'd say it's more a case of you getting used to the slightly different position of the blade center under your feet and a new(ish) profile. A different suggestion from me is for you to go for a casual skate with your laces untied, this will really quickly attune your foot to the center line of the blade under your foot.