Prethinking can actually slow you down in CR because not only is it unnecessary but also it can distract you from seeing the correct answer and tempt you to choose an incorrect choice. So, one move you could try for speeding up in CR is to stop prethinking and rely on careful analysis of the relationships between answer choices and the passage to get you to correct answers.
Regarding your question about practicing with OG questions, I think you're correct in suggesting that you may be better off doing something in addition to that, such as studying some Verbal concepts and strategies that could help you get more questions correct.
Regarding which resources to use, TTP provides some good strategies for both CR, RC, and DI, and if you were to sign up for TTP for a month, you could also use it to strengthen some Quant topics.
You could also use YouTube videos to get insights into how to answer Verbal and DI questions.
For tips on how to prepare for Verbal, and to an extent DI, effectively, see these posts.
How to Prepare for GMAT VerbalGMAT Critical Reasoning - Trap Choices Versus Correct Answers