GCC 2.95 is included in Sony Linux and Blackrhino and can compile Linux 2.4, but not Linux 2.6 because of a bad coding style in Linux 2.6. It is possible to change the coding style of Linux 2.6, but you need to change very much code.

GCC 3.0.3 is avaible from the Sony Linux side for PS2 Linux. As far as I remember it is still not possible to compile Linux 2.6. I heard that this version has some bugs.

GCC 3.2.2 is used by ps2sdk for compiling homebrew. For homebrew I would say it is working good. In this version the Linux support is disabled, so neither Linux 2.4 nor Linux 2.6 can be compiled. Otherwise I think it would be possible to compile Linux 2.6.

GCC 4.2 was used by Chewi for gentoo. This version causes assertions to fail in the compiler. Chewi reported that he was able to compile working homebrew software.

GCC 4.3 was used by Chewi for gentoo. I don't tried this. Chewi said that it has more support for R5900 stuff.

Another GCC 3.?? was used by Chewi for gentoo. This was never running good.

(http://forums.ps2dev.org/viewtopic.php?t=10156&start=420)