I've been considering this question too.
I don't think there is an easy answer that will suit everyones situation.
As I understand it we have paid zero for the IMOUE's if we got allocated them in the SPP, so selling them means we have tax liability for the full amount at the point of sale.
I'm not sure if we get 50% CGT relief upon sale after holding them for 12 months, although I have been informed that if we convert them to full heads the CGT relief clock starts then and not when the options were allocated.
So, I guess it will come down to the most favourable choice of two calculations when the price hits your target and you're thinking of selling some.
The quantity of options you'd need to sell to receive enough dollars to convert the balance to heads.....
VS........
The quantity of heads you'd need to sell to convert all your options.
Either way you'll end up with X amount of heads and a varying tax liability dependant on what you can offset as CGT relief along with whatever else is assessable that particular year.
Happy to be schooled in this as am a newbie to options and just feeling my way here.
