ないまでも・はおろか: the difference
ないまでもN1
Meaning
May not … but
Past papers
Tested once in past papers
Example
これは不可能ではないまでも、実行するのは困難である。
This may not be impossible, but carrying it out is hard.
はおろかN1
Meaning
Let alone, Much less, Needless to say, Not to mention, Not only but also
Past papers
Example
「ルームメイトはオムライスはおろか、おにぎりさえ作れない。」
'My roommate cannot even make onigiri, let alone omurice.'
How to tell them apart
「〜ないまでも」: the high goal is missed, but the lower level is met.
「〜はおろか」: not only the high goal, even the most basic level is not met.