Some Linux distros have already switched to using xz for compression over gz as it compresses significantly better (Fedora and Arch Linux, for example). If you've ever used 7zip to compress files on Windows, xz is based on lzma that 7zip uses.

Compression statistics: http://pokecraft.first-world.info/wiki/Quick_Benchmark:_Gzip_vs_Bzip2_vs_LZMA_vs_XZ_vs_LZ4_vs_LZO

It's licensed the same as gz which BOINC uses natively, so why not switch to xz now? Projects like Clean Energy Project have extreme network bandwidth requirements because of the use of gz instead of xz.

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Main Comp: AMD FX-8120 4GHz + R7950
Others: Phenom II X6 @ 3.5GHz x 3 + R6850 x 2