Updated and tried ECW-slotting again after about a month. Slotting problem seems fixed.
There still is a process eating 100% of a single core, but it does not block the rendering.
off-topic: I have had troubles with the launcher since its existence giving me errors and (for example) saying I'm not logged in, but when I start it anyway the game shows I'm logged in and all modules are available.
With the adjusted graphical settings the stutter is gone; even when flying through the guts of the Phantom:
Solution by @Rapierarch:
PS Closest I have ever gotten to a Tomcat (not close enough to reproduce):
tribbin's post in Slotting on ECW practically impossible (especially with VR) on ECW was marked as the answer