Opinions please?

[BrianG]

The only reason to race with larger cap batteries that I can think of is to get the most out of the batteries. When you discharge close to the max continuous rating of the batteries, you don't get the full capacity, Ah-wise, that you would if the batteries were discharged at, say, half their max C discharge.

For instance, if you have some 4Ah batts rated at 15C (60A) and you discharged close to 60A, you probably won't get 4Ah out. Whereas if you had 4Ah batts rated for for 30C (120A) and you still discharged at 60A, then you'd get closer to 4Ah out of the batteries, which would translate as extra runtime.

Either way, we're only talking about a couple minutes extra at most in the example above.

In your case, since you are racing times so close to the runtime of the battery, it could mean the difference between finishing first or last if they die 1/2 lap left to go. Differences in ambient temps and slight changes in how much you gun the throttle can change the runtime too. Personally, if I was running that close, I'd go with 6Ah to be safe, but that's just me.