Here's a simple test I ran last week. Rendered in C4d with aa set at best. Took 1 min 29 sec. I haven't tried a lot of trees, yet. But the meshing and maps were set to be a higher res which helps a lot. Ignore the big lumps in the background.. they were an experiment that failed.

I used ozone for the atmosphere, and the rest was exported from pro.

One thing to note; not all terrain maps generated by pro look as good as the ones presented in this thread. It seems pro doesn't use the bump settings for a material when it generates the map. For some terrain materials, the bump settings are very important. Sure hope this is something e-on can change.