Well, I finally bought the kinvara 5's. And to give an update for future people having the same problem. These are my findings after my first 24kilometre / >half marathon run.

- I could immediately feel the weight difference with my old omni's, which you can really feel. I don't know if it's just me, but I felt like my cadence went up by using these shoes (e.g. from 150 to 180).
- The damping is basically the same as the omni's if you land mid foot. However, the omni had an annoying wedge at the medial side of the foot for anti-pronation. In these shoes, you can definitely feel that this wedge is gone and my landing now feels more natural.
- The feeling of speed and flexibility is a lot higher in this shoe. It doesn't feel like a sponge but a lot more responsive. On downhills, you can however also feel that it's a bit more stiff, making proper running technique on downhills even more important (my run had some 370 meters of vertical height in it).
- They really fit well. Fit in front is however slightly more snug than you would expect at first. But no irritation during running at all!
As for feeling differences in impact on joints or muscles. At the beginning of the run I indeed felt that the drop was a bit lower (going from 8 to 4 mm), but this wasn't all too troublesome at all. It did however tire my calves a bit more at first. During the run I also felt that the knees get a slightly bigger impact, especially on downhills. Post-run, the knees also felt slightly more sensitive.
Thus, overall nice shoes. It is a difference from guidance shoes but if you have a proper midfoot / front foot landing technique, the switch shouldn't all be too dramatic in my opinion. I have to admit that this is my first run impression, so it definitely might change in the future. But for me to update, the weather will need to cooperate during the run next time. I hated the wet horizontal snowfall which I had this time..