for example when a scene is just loaded and you turn back to see not visible until now objects then FPS drops significantly while not rendered earlier textures come to play
is there a way to render new textures smoothly, without catastrophic FPS drop?
Since both OpenGL and DirectX require that textures have power-of-two dimension, consider resize your images to meet this requirement.
Just to be clear with that... If I have 1000*1000 texture and do resizing to 1024*1024 I do not get any FPS-boost?