Well, we're talking about 3.7M pixels for the E3 and 4.6M pixels for the Vive Pro so that's 25% more pixels. Apart from that the E3 uses a single simple mobile display panel while the Vive Pro uses 2 custom panels, so I'm sure the amount of used pixels is (much) higher for the Vive Pro, maybe effectively around 40% more.
Regarding the Pimax 4k, it has a higher resolution panel but pixel usage is WAY lower. So I expect the Vive pro SDE to be somewhere in between the E3 and the Pimax 4k, being closer to the Pimax 4k. I hope it's not going to irritate me but I think it wont. Of course much depends on the pixel layout, like you said, but we'll see.
I never really used the E3, the ergonomics are HORRIBLE (it's really a torture device for your head) and the SDE was just a bit too pronounced.