@Amrch
600D can already do 1736x696 5x3 @ 60 FPS (in 720p), patching this mode to make it sample the sensor in 1:1 is possible (1:1 is like x5 mode), but it's not implemented.
After patching 720p mode to 1:1, you will have 1736x696 in 1:1 (square pixels), from that you will be able to lower res down to 320x240 and get 60 FPS.