C rating doesn't slow down an RC. All the C rating shows is how much sustained amps the battery can take. A higher C rated battery may have a bit more punch, but it's the volts that determine how fast a motor is going to run on a paticular battery, and all 3s batteries deliever 12.6v at max charge.
I would just use what you got for now if money is an issue, then later on buy an actual HW esc and throw in it. Unless you are a diehard racer, there probably isn't much you really need to mess with using a program card that you can't do with the button.
But yeah, a lot of things in this hobby...