IPD is important for clarity. One of the Oculus setup exercises involves adjusting IPD until lines of a cross converge properly and are focused, and small adjustments can make a world of difference (to me they did, anyway).
Not suggesting your VR isn't set up properly as it sounds like you have put the necessary effort in but I do wonder sometimes how many people just slap the HMD on and expect VR to look great with no tweaking. The initial out-of-the-box experience with the Rift in AC was amazing from a 'wow... I'm actually IN this car...' perspective but the IQ was a shimmering, aliased, low res mess. After setting it up properly I find the IQ great. Of course my 4k display is better, but that is literally the only thing that IS better, and it's nowhere near enough to make me want to sacrifice the incredible immersion, stereoscopic vision, freedom of view, depth perception, sense of scale, placement of objects in 3D space, the overwhelming sense of being in the car, on the track, at the venue. Looking at a 2D screen with a static PoV with the rest of the room visible around the edges... man, it's kind of pathetic to me by comparison. I wouldn't want to use VR to play, say, H:ZD but for racing sims where immersion is key I can think of nothing better.