Shift Register 595 Library

CrossRoads:
I suppose having all outputs change together on the RCLK after shifting a bit in is somewhat better.
But since only 1 bit is changing, I'm not sure you'd see much difference.

I don't understand exactly what do you mean.
Look, my task is to drive shift register via 2 signal wires (clock and data), do you have any better idea how should I do it?