How to set autogen and I question about percentages

Well, in that case setting the trees to something like 2500 might help you! You keep all the houses and only lose a bunch of trees, afaik only and mainly in big forests. To me this is the best compromise so far. Cities still look great with all the autogen, only huge forests are less dense. But at aa certain height that doens't bother me, specially not when using nice textures like FTX.