Saying that you are going with more voltage for longer runtime can be a bit misleading. If you are going to run higher voltage, you have to setup for it from the get go.

The advantage of running higher voltage is to reduce current draw. As current draw increases, so do inefficiencies. These inefficiencies (losses) are the source of most of the heat generated in a brushless system and the heat is a sign of wasted energy.

If you take a 4S system that turns a maximum rpms of 30,000 you will get a certain amount of current draw while accomplishing a specific task. On the other hand, if you take a 5S system that also turns a maximum rpms of 30,000, the 5S system will be doing the same amount of work as the 4S system with a substantially lower current draw. Since the current draw is lower, there are fewer losses and less heat. Everything runs more efficiently.

In real world application, it's harder (for me) to figure out exactly what battery to go with when going to a 5S configuration. When running 4S I usually run a 4S2P 8Ah pack, so I have about 118.4Wh of stored energy. When running 5S, I should be able to go to around a 6Ah pack and get the roughly the same runtime, with some gains due to less stress on the pack resulting in less voltage drop. Although these gains may be debateable, since you've gone to a pack with less capacity and we don't know how the load will affect the voltage drop.

It all seems to go around in circles to me at this point. Assuming that the 4S 8Ah pack can deliver 20C, which is 160A and the 5S pack can deliver 20C, which is about 120A, each pack is still going to be stressed just about a like in either system. To me, the only real advantage is that the whole system will run cooler on the 5S setup than it will on the 4S setup.

What kills the whole deal with 5S for me is that the nicer motors run cool no matter what, whether they are being run in a 4s setup or 5S setup.

Oh, I also liked the idea of being able to run a cheap 5S2P 8Ah battery pack because the current draw was so low that it didn't stress the cheapie 10C pack. Of course, the battery is a brick and I can't race with it because it knocks my suspension out of whack.

I personally think that it is pointless to beat your brains out over the 4S to 5S issue. I've found 4S to be great in the right setup.

I don't think that going to higher voltage will really payoff until we can reliably run a 6S or 8S setup that only draws 60A peaks so that we can run cheap battery packs without stressing them out. That's on the practical side.

As I said, all of this keeps going around in circles. For me, I am satisfied for the moment with 4S systems. They are a good compromise among weight, runtime, heat, and cost.

Once technology catches up, then I'll turn all of my 4S2P packs into 8S1P packs and run much lower kv motors just for the efficiency.