Is SpeedIndex expected to be the same for Cached View as well as First View?

I was just noticing the fact that for most sites it seems the speedIndex is roughly the same for both repeat view and first view. Is that logical/theoretically expected?

Not necessarily, it depends on how well they do at caching content. This huffington post page differs by ~30% for example:

They will usually be relatively close (not an order of magnitude faster) as long as the base HTML still needs to be delivered and if they are reasonably well optimized.