...(bout 10cm per pixel for heightmap as a guess) I can only render up to 800x600 because it's a free version of the software I use, allthough I could render a few different angles and stitch the images together if anyone wants it any higher...
I... seriously doubt that you're using that kind of resolution.
If Earth has a circumference of about 40,000 km, and you're using a 8192x4096 resolution texture, one pixel at equator equals to about... 5 km detail on the surface. 4096x2048 res texture could have 10 km per pixel on the equator; that's the resolution I use for my GIMPed planets. Even if the planet was quarter the size of Earth in diameter, it would still have equatorial circumference of about 10,000 km, and a 8192x4096 res texture would have about 1.2 km/pixel detail level; 4096x2048 would have 2.4 km/pixel.
Unless the program is using procedural shaders for the surface, there's no way the texture could be of that detail - it would probably fill a good sized room full of HD's at that detail level. For earth sized planet, the texture size should be about 400,000,000x200,000,000 resolution - the closest powers of two resolution would be 2^29x2^28 (536,870,912x268,435,456); at 24 bits per pixel, that corresponds to 3.45876451*10^18 bits, which is, according to Google, 393 216 terabytes... if you had one terabyte HD's, that amount would be in a grid of HD's that was 73x73x73 HD's per side, plus the odd 4199 HD's. That's a lot of data storage...
Perhaps 10 km was what you meant... instead of centimetres...?
Regardless, it looks rather cool. Also, for rendering you might want to try some free 3D software like Blender - you already have the textures if I'm not much mistaken,
