I always felt that Provia actually came closer to Kodachrome than Astia. Astia is just WAYY to low in contrast and too unsaturated. But regardless, I still think Ektachrome E100G comes closer to Kodachrome than either. And some people say Ektachrome E100GX is the closest you can get to Kodachrome in an E6.
Here are a few examples of the "wayy low in contrast" of Astia:
(click on image for larger)
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This was K64:
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Like I said: pick a new roll of Astia, expose it bang on 100 ISO (ignore all the old advice to over/under expose it), and check the results.
To me, the latest emulsions are right up there with the best Kodachrome could produce. And it scans with even smaller grain than K64!
I've tried E100GX and it's nowhere near as colour true, although it can be as saturated as Astia. Have not tried E100G recently.
Fuji is constantly improving their film. Sensia 400 for example is nowadays one of the best high speed colour negative films I've ever seen. It used to be cheap and nasty, not anymore. In Winter, I use it almost to the exclusion of anything else: it just works wonders with the lower levels of sunlight.
I don't know why they do this and why so low-key advertising of the changes, but I've seen consistent enough changes to warrant a switch.
Of course: YMMV.