Paul thank you so much for you time and patience.
Yes, I am considering the option of 1:4 ratio. The spec sheet for the LEDs I have suggests a peak forward current of 50mA. Is it safe to push it to this limit in the 1:4 ratio, or should I be dropping it even further (if the intensity is still ok)?
I see what you mean about non - linear. That's why from 20mA to 12mA I can't really see too much difference. I never knew why.
Yes I did connect a separate pwm pin to each digit common. I'm not too confident however using a shift register. I'll do more homework on this then maybe ask you some more questions down the track once I've studied up on it (if that's ok).