Note also there will be a wide variation of timings across components, a wide variation of chip sensitivity, and a sensitivity to clock speed, temperature, power supply voltage, data rates, etc. etc. This approach is "O.K." for a hobby project, but it would be a very bad idea to try to use it in a commercial project, especially anything that might see volume.

Not to rain on your parade, but given you can get PIC devices with fewer pins and at lower cost than a 74HC595, you would be further ahead to create a dedicated display driver PIC that you can send data to by 1 pin serial. Fewer components too, and rock solid communications.