I reinstalled my computer 3 times now (twice for FL, once because I fiddled too much with components without restoration points... What an idiot). Tried multiple drivers, can't do much with DirectX since it comes packed (version 11 of course.) with Seven, the only thing I can do is upgrade it (DX8, DX9 and such only say "A newer version is already installed" and because it is integrated in Seven, I can't uninstall it. Microsoft...).
I've got everyhing the game need, benchmarked my CG to find if it could mess up textures and couldn't see anything wrong. FL is the only game who fail to render HD textures.
Hm, I also had troubles with the game BULLY and had to patch it as the textures jacked up because of my RAM being way above the game limitations. Maybe FL is having something relative to it ? I have 32gb RAM, could the game don't know how to handle it ?