I think if you want to run 6S - get a 6S pack. It's generally lighter and easier.
Running higher capacity packs give longer run time, but being heavier, compromises the handling.
So in most regards, the lighter the better.
My Onyx Graphene 6S 5200 packs are punchy and give decent >10 minutes of run time.
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I also run a slightly smaller Gens 6S 4500. It's rapid on this.
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And on my Onyx 6S:
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Beast of a car.
4S in many ways is more sensible. It takes less of a toll on the rig and is still fast without being bonkers.