hey @lukasgraesslin , I agree with the others about some suspected elbowy / DSX-y motion creeping in at the higher speeds.
Now, since you mentioned consistency, it would be good to see what happens when you try to play some DSX licks (i.e. only changing strings after downstrokes) with the exact same motion. Are you more consistent there? Do they feel easier?
If so, it may be further evidence that this motion is indeed more biased towards DSX. And the consistency problems may be due to you thinking that you are doing one thing, while doing another