The extra caps help, but are mainly to help ripple current, which is generated mainly on brake and off throttle. There is very little in the way that such low capacity caps can do for actual punch, though of course in theory they help a little in that regard as well. All of this means you beat up the battery less with less stress on the battery, so over time they last longer and everything else runs cooler too since your external caps are sharing in the load of the internal or "on the board" caps (such as found with the HW and Tekin ESCs). I find the Tekin RX8's don't NEED an extra cap bank, but doing so can let them use not as good batteries without getting hot, or can drop temps for longer runs, and is of course nicer to your batteries.
As for batteries, IR is best when warmer and at higher voltage, which is why a larger pack is almost always much better than a higher C pack, as it maintains voltage longer, keeping both IR (C) and temps low while voltage up. This also translates into a cooler running ESC as it needs less amps to put out the same wattage (this is why 4s or 3s systems run cooler than 2s systems that are providing similar amounts of power). This is why I always suggest 7000 or larger batteries as a result for 2s 4wd SC, even if you're only running 5 minutes and only using 2000-3000mah of that pack depending on track and trigger finger.