It won't hurt framerate but it could potentially increase the little stutters when new plane textures are loaded. Disabling custom skins might help there.
If you get a lot of stutters, try finding the pci latency tool mentioned in some other thread, and reduce the vid card pci latency from whatever it's at to 128 or 64. That has helped some people because it reduces the wait time for everything else in your computer including (in many computers) the hard drive controller. I'm using it and like others have reported, it let me run even 1024 textures without the huge stutters we used to see with the bigger texture sizes.
But again not preloading textures should not affect framerates. Reduce the texture size if necessary and if you get stutters, try the pci latency tool.
edit - here is the pci latency tool.
http://downloads.guru3d.com/download.php?det=951