Unless you're speaking in Latin, you should split your infinitives if you wish. That "rule" makes no sense in English grammar, even if some people's grade 4 teachers told them so. The classic example of "To boldly go ..." is *not* ungrammatical in English. This is a Latin rule* that is applied to English when it shouldn't be, with the thought that Latin is a better language.
* It's actually hardly a rule in Latin, as infinitives are single words, so they can't be split. "To go" is one word in Latin, so it's impossible to split. It's perfectly possible to split in English, and not necessarily ungrammatical to do so.
<end linguistic rant>
(If anyone wants to argue on this point of grammar, you had best produce a sentence diagram showing a split infinitive to be ungrammatical in English.)