Great question - and the answer, honestly, is "that's above your pay grade". This question:

https://www.beatthegmat.com/og-10-question-t16968.html

Is a perfect example. That decision between "so x that y" and "so x as to y" is the bait in this one - it's what the GMAT is using to distract you from a relatively easy verb tense issue. I use this question all the time in GMAT seminars and classes to show people the importance of knowing what you do well (verb tenses, modifiers, pronouns, agreement) and focusing on that. Ironically, the people who study the most for SC tend to get this question wrong the most...because they're trying to apply obscure rules of grammar that they just can't hope to master while also figuring out Data Sufficiency and Critical Reasoning.

There may be some extra grammatical distinction but really for our GMAT purposes these two expressions are interchangeable. Wise test-takers will steer clear of that and look for a more common decision point.

Check out this blog post for a similar question and breakdown: https://www.veritasprep.com/blog/2010/1 ... ect-idiom/