I was a fast track student. Things to consider are:
1. Your undergraduate CGPA is a general measure of your ability to score on standardized tests - this doesn't always translate to research capability. I know people who have dropped out or fell back to a Masters because they lost interest and/or had difficulty conducting research.
2. Be selective of your supervisor - working with one that has prior experience in handling fast track students is important. What you want is someone who has the capacity to monitor you during the formative months before granting you the independence most PhD researchers are accustomed to.
3. Be prepared to extend your duration of study - in an ideal scenario, you want to graduate in 3 years or less, but you do need to give yourself sufficient time to master the basics or it'll cost you in the future. Fortunately this is easily remedied with good time management - schedule everything and stick to it!

All the best!