I've found that Maya doesn't really play well with compression. Even with RLE compression on a targa, there are cases when loading it into Maya takes a long time. (Which is to be expected, as it has to un-compress the file each time it want's to read it)

It's a trade-off really. You either get smaller file sizes, or faster load times. With small images this is probably negligible, but once you get into 8k textures, it can become a problem, especially when you have 100's of them.