Texture Resolution

I've always run at 4096 x 4096 textures but am getting heavy performance hits in the bigger cities at 8x MSAA.  Does this setting have any effect on ground textures or is it just for airport textures, etc?  I've tried running at 2048 or lower and it could just be placebo but at 4k the ground textures look much better to me.  I run ORBX global, vector, and LC if that matters.  Does the texture resolution have any noticeable hit on FPS? This is for V4.

Thanks!