This topic is relevant to my interests and you are doing good work.
thanks for all the praise, and especially to Axem for putting it in the newsletter 
got myself a new 4GB memory module today, so my renders will be better in the future, yay!
(seriously, blender needs 8GB of RAM + 32GB of virtal memory for compositing 4k*8k images? WTF?? )
Sounds about right, big images take a lot of memory and when you run out of RAM the paging to HDD will slow down process quite a bit. This happens especially if your Blender scene uses layers and compositing in render settings, which pretty quickly causes cumulative memory use at high resolutions and high anti-aliasing settings... and especially if you use high-resolution textures for the render scene itself.
This is one of the reasons I would advocate (and why mods like Blue Planet) use cubical skyboxes instead of spherical textures.
I don't know what workflow you are using, but assuming you have your scene set up in Blender, you can always render it in cubic format as well as spherical. The amount of work to set up the skybox is a bit higher, and I'm not sure if the cube can be used in p3d to show them off quite so conveniently, but the benefits are significant.
The best thing is that you don't need to deal with monumental individual files. Six files sized 2048² will offer about the same visual quality as a single 8192x4096 texture, while using 25% less memory in total - and I think you'll note that six 2048² files are probably faster to render than a single large render, because the individual renders will not be hampered so badly by the page file use.
Another major benefit is that a 8192x4096 sized texture requires a video card that supports at least 8192² texture size, while a cubic skybox of same quality can be rendered on a video card that supports meager 2048² texture resolution - which is practically all of them by now.
The added benefit is that you can also render a cubic skybox at 4096² resolution per side, which will provide effective resolution comparable to using a single 16384x8192 spherical texture... without the need to
render such a massive texture (although you may still need to use textures of such resolution FOR rendering). I'm sure you can appreciate the possibilities...
But keep up the good work, any spherical texture you make can be pretty easily converted to cubic format any time someone would like to use them in game.
