You are right Roff, the 10ohm emitter degeneration resistors would be a good idea. I was honestly wondering how much of an effect beta would have, as I've never bothered measuring it within a batch (honestly because good people like you point out that an emitter resistor would be a good idea, and make the design a lot more independent of beta
). There are also more complex type current mirrors that are more beta independant, but that would add some additional transistors.