Trigger and Wingracer are correct. A truly higher C lipo will have lower Internal Resistance, and will provide a higher voltage under load, thus better performance.

The difference is small but clearly noticeable. Will likely only be of practical benefit if driving is up to par though.

I know it's counter intuitive, but generally with the exception of 4x4 short course, competitive stock racing requires far better batteries than modified. Modified can just use a faster motor, many use low C lipos to take the edge off of hot mod motors to make them a little more driveable even. 4x4 short course is perhaps the most common exception, they need great lipos just to survive due to the high amps required.

The difference will be most noticeable under acceleration when the current is highest, less difference at top speed but still something.

One caveat, higher C lipos are heavier, if the car is above minimum weight then the heavy battery might not be the way to go, especially on road. Off road weight is less critical, as it can have some beneficial tradeoffs in the bumpy sections and such.

There is a lot of concern regarding C ratings, some brands are pretty straight up, some not so much. That certainly complicates and muddies the whole subject.

Besides track performance perhaps the best way for the average racer to help separate fact from fiction is to invest in a quality charger that features IR measurement. Simple but generally effective way to compare packs, and track their performance over time, help determine when new packs are justified, etc.