As said above, Open Clouds is no longer freeware.
But you're not missing much, most of the times the weather with Open Clouds was just looking terrible, and it was not sorting any of the problems of the default weather.
So keep with the default "Real Weather" stuff, it's good enough.
For the cloud textures, to me there are only two alternatives:
1 - the HDE clouds textures from Pablo Diaz, they look really good. The original package was made for FS9, but the cloud textures are compatible with FSX. The original sky textures are NOT FSX-compatible ! But a new version of those sky textures were uploaded to Flightsim.com, with explicit FSX format.
2- FS Skyworld 2004: REX little brother for FS9, but once again the clouds (and ONLY the clouds) are compatible with FSX. The textures are in lower resolution (512) but you get a LOT of choices, with a graphical interface. Some of those clouds look really good, and they are quite FPS friendly.