7zip is not usable on older systems which have low amounts of ram. Otherwise I would probably use it. (I have some legacy machines I use for developing and testing.) I have been bugging the UPX developers to make the --exact switch really make files exactly as they were (byte for byte) before compression. I have done some tests with it as is, and with .exe, .dll , .ocx and .scr files it gets far better compression ratio than either winrar or 7zip if the files are precompressed with all options including the resources. This could be scripted inside a batch or cmd script to uncompress the executable files, and make the compression ratio even higher. It would also allow for compression of windows component files and other things which have crc checks and must not be modified in any way. The AbodeReader installer uses such a technique with a modified UPX, to obtain it's very small installer size.