Cogger I would probably say the only reason to get the Aspect vs. Scale is if you for some reason wanted a lower end groupset and an overall lower end frame. The Aspect is sort of their budget mountain style bike whereas the Scale is a dedicated XC Hardtail. I would own a scale if I wanted another hardtail but I would rather get a Spark as I don't currently have a FS bike.

In terms of seatpost size that doesn't matter for you because you will need to get the right size for your bike and they may not always be the same across different models even from the same brand and especially across different years and travel will be determined by your personal fit which could be different from the OP.