Personally, my '96 Cuban Partagas Lusi's from the POS factory are unsmokeable unless they are between 63.6%-63.8%, otherwise they taste so...tobacco'y.
:r
Seriously, try it out, if they draw and smoke good, that's all that matters (as long as your between 55-80). I actually do think some smokes tend to be too loose of a draw below 65% and some too tight above 70%, but I wouldn't swear by it.