GNOME: Fast change resolution and refresh rate

xrandr is a powerful tool that can list avaiable mode,
and change resolution and refresh rate without restart X

# xrandr
SZ: Pixels Physical Refresh
*0 1024 x 768 ( 321mm x 241mm ) *70 60
1 800 x 600 ( 321mm x 241mm ) 60 56
2 640 x 480 ( 321mm x 241mm ) 59
3 1024 x 576 ( 321mm x 241mm ) 60
4 720 x 576 ( 321mm x 241mm ) 56
5 856 x 480 ( 321mm x 241mm ) 59
6 800 x 480 ( 321mm x 241mm ) 59
7 720 x 480 ( 321mm x 241mm ) 61
8 512 x 384 ( 321mm x 241mm ) 60

# xrandr -s 800x600 -r 60

Thanks Joseph's hint