Your first shot could benefit a lot from a CPL at least, which would probably save the sky. And perhaps a GND to bring up the shadowed areas on the right while not overexposing all the foliage and sky.
While Velvia is certainly much easier to shoot in the golden hours, it's quite possible to shoot it in full sun (scattered clouds or a fine touch of cirrus are lovely) using a CPL and the Sunny-16 rule; e.g. 1 2 3 (not LF though).
When I shoot with Velvia 50, I rate it as ISO40.
Overcast or diffused light is the key to pleasing smooth exposures and good scans, and rarely any sky included. If I saw conditions like the images posted here (except for the golden trees on water), I would just pack up and take a nap. Ain't worth fighting with your film, and scanner later on, only to get poor results.