60/65mm vs 80 mm spotting scope for backpack hunting

[Arrowhead]

I'm interested to hear opinions on 60/65mm vs 80mm spotting scopes for backpack hunting (mountains or otherwise). I know from some posts on the For Sale section that some are selling or trading their 80mm spotters for lighter setups. Others I'm sure feel the extra low light performance of the 80mm versions are worth it despite the extra weight.

Opinions please.