Thanks for your input so far Enopho. Anyway after some time away (and improving PC thermals) I've been able to jump back into ED VR for some more testing. So far I've found some fairly good settings that seem to work for me. I won't go too much into details on settings ingame but all terrain and shadow settings and sliders are at ultra/max while some other things have been turned off. SS and HMI are both set to 1.0.
I just changed from piplay version 2.X.X to the latest 3.X.X. I'm also using the latest nvidia drivers. Personally I don't have and issue/don't notice the ghosting and microstutters. Don't get me wrong, there is ghosting but not to the point that it bothers me. I did however notice that with the latest piplay, ED/piplay do seem to be able to utilize my GPU more. I'm seeing usage up to 95% compared to rarely past 70% before. I have less FPS issues/drops now even with higher settings.
Piplay slider is set to 3. Now comes the interesting part. In steam VR settings (regular version, no BETA) I've set the sliders to 20% in programs tab and 160%-170%SS under video tab. This seems to be the sweet spot for me at which I'm also at a constant 58-60FPS, even with OVRdrop running.
When both sliders are set to minimum, 20%, the quality inside ED is terrible. Eventhough Piplay has its own rendering, steam compositor definitely has an impact on quality aswell. At least for me.
Obviously I'm stacking SS here but it seems like the 1080Ti can handle way more than Piplay slider at 3 and steamVR at minimum. An even higher quality might be attainable if piplay could be set to higher than 3.
The main difference I see with higher versus lower SS settings is jagged edges. I've taken some pictures through the lenses where you just about can see the difference. Needless to say pictures through the lenses aren't optimal so don't look too much at the overall quality, it looks better than in the pictures. The examples are with steamVR set to 400% and 100%. Obviously at 400% FPS is terrible, 30FPS, but this is merely to illustrate.