"Ideal amount" of course is relative to Rider Hight / inseam lenght. The absolute numbers of dropper post travel do not tell much, unless you take framesize/rider's hight/proportions into account. For me (168cm tall / 77cm inseam) it's 150mm. Could go longer, would not want to go shorter on dropper post travel!
For me (168cm tall / 77cm inseam) it's 150mm. Could go longer, would not want to go shorter on dropper post travel!