Infinitives is an to+action verb combo i.e. to go, to eat etc.

When someone angrily yells "Go to --" probably you know what place they have in mind. But with infinitives reader's do not necessarily know what to follow. Generally if possible one should let the action immediately follow the verb, but sometime exceptions are allowed such as situation in which you want to add emphasis. Take for example:

To control this situation really, the supervisor must be at site. : Awkward
Really to control this situation, the supervisor must be at site. Better
To really control this situation, the supervisor must be at site. Add emphasis

As far as GMAT uncle is concerned he will not test you on split infinitives from such perspective as added emphasis. It should be your call, in general.

Though as you know 2+2 is 4, to + verb is an infinitive and do not choose an option that un-necessarily split them. Help them keep united and GMAT god will bless you!!

arora007 wrote:How would the GMAT treat this split infinitive ?

She used to secretly admire him.

https://www.oxforddictionaries.com/page/147

I don't recall an instance of a split infinitive in the OG, but that doesn't mean it's not there. Given the way the GMAT handles other things, I think the cited site's advice is the best we can do:

As a result, it's safest to avoid split infinitives in formal writing, unless the alternative wording seems very clumsy or would alter the meaning of your sentence.