I've got alpha's in both and typically the 8x are more forgiving to heat, shake and low light....10s have a bit more mag, but it's just that....a bit. Not a "WOW, that's 2x bigger".
I found 12x leica to be useless without a tripod.
I had my Meopta 15's for four years and never used those on a tripod even once.
Man I can hear the collective shudder of every Arizonian