This is how it looks when I grep for SGI on my Mint 14 installation where 3d is working:
mint apps # glxinfo | grep SGI
server glx vendor string: SGI
GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer,
GLX_SGIX_visual_select_group, GLX_INTEL_swap_event
client glx vendor string: Mesa Project and SGI
GLX_OML_swap_method, GLX_OML_sync_control, GLX_SGI_make_current_read,
GLX_SGI_swap_control, GLX_SGI_video_sync, GLX_SGIS_multisample,
GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, GLX_SGIX_visual_select_group,
GLX_OML_swap_method, GLX_SGI_make_current_read, GLX_SGI_video_sync,
GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer,
GLX_SGIX_visual_select_group, GLX_EXT_texture_from_pixmap,
GL_EXT_texture_edge_clamp, GL_SGIS_generate_mipmap,
GL_SGIS_texture_border_clamp, GL_SGIS_texture_edge_clamp,
GL_SGIS_texture_lod, GL_ARB_framebuffer_sRGB, GL_ARB_multitexture,
mint apps #
So some SGI might even be normal in glxinfo.