For those who read this and might want to give it a try: the HDEv2.1 pack is in fact the HDEv2" pack with a small modification: the sky textures got modified to become compatible with FSX and P3D.
The original HDEv2 pack is made for FS9. While the clould textures are already compatible with FSX and P3D, the sky textures are not and will produce terrible graphic glitches.
So FSX and P3D users, ensure you get the HDEv2.1, not the HDEv2.
Last remark: the cumulus clouds, which are all in one single file (cumulus.bmp if I remember correctly), are offered in multiple resolutions.
I strongly encourage you to give a serious try to the medium resolution: 512x512 DXT3
A resolution like 512x512 might sound extremely low to you, but I assure you it already gives very beautiful clouds (much, MUCH better than the default ones), and they are very light on the FPS, allowing you to push the cloud coverage and cloud draw distance further, resulting in a more pleasant weather rendering
