Thanks for the advice. I've deleted the newest drivers and gone back to drivers which were released in June but it hasn't made any noticeable difference.
The pop-in looks like extra layers of detail being added to the planet surface and the outer surface of stations. It looks as if the textures are taking a long time to load.
Would a clean install of windows help this?
Hard to say what the problem is with the limited info, but before doing anything too drastic it would be worth fiddling with the ED settings. Start by increasing the model draw distance to max and reducing the terrain detail to about a quarter. Also FOV at 3/4's which is wide enough for VR. Then try the game - disregard lag any caused by increasing the draw distance, as this should be addressed using other settings - just concentrating on the "pop-in" of surface textures ATM.
If this solves the "pop-in" (or at least significantly resolves it), then can address any lag by turning your attention to the FPS. In that respect, I'd start by using FXAA (not SMAA) for anti-aliasing, medium shadows, SS at 1 (assuming you are using the SS in Oculus Rift at 1.5) and HD at 1.5. Switch off bloom and DOF. That should be about right, but if you are still experiencing lag then (a) use ASync projection in your headset and (b) change some of the other game settings to medium one at a time starting with those that are least important to your game experience e.g. galaxy map, neutron stars, etc. If still not happy with the result and don't want to go lower on the above settings, then put terrain details right down as it is (I think) hard on the CPU and you only have an i5.