Trains1213_YT
The final question is "How much do you believe the manufacturers C figures?"
There is more than a little evidence that extreme C figures are more for marketing than being factual. The manufacturer does not state the effect on the battery or its life if you do discharge it at the rate claimed.
For example if you using the majority of the battery capacity in say a 6 minute flight that's an average discharge rate of just 10 C. In this case even a 20 C battery will be able to easily provide twice the average flight power in short bursts. Using a 120 C battery will make no practical difference apart from the cost of buying it in the first place.
It is possible that a higher C battery might be better made so runs a bit cooler and may last a bit longer but nothing is guaranteed.
As Merv suggests there is no need to buy 'more' than you actually need.