In GTK file chooser, if icons were assigned according to item attributes (type, name, extension), it would be very fast.

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Many people still have a slow computer, many files or simply want an immediate respond from user interface.
GTK file chooser is an example where huge performance gain could be achieved if icons were assigned according to attributes, not content. This is a main reason why file chooser is so slow and several seconds reads something from the disk. 

In previous versions of file chooser, some people complained that nothing is visible until all items are scanned. Now it is "better", because you can watch the progress of building list, but in the meantime it is unusable anyway.

I have just tried to make a file lister in PyGtk, which shows a fullscreen listing of filenames, extension, sizes, mtime, atime. Here is the speed:

3272 Items in /usr/bin 0.49587392807 seconds
Half a second. Now try opening /usr/bin in GTK file chooser. Please, would it be possible to add an option which would disable the MIME type checking according to content? Would it be too much *NIX violation?