If there's spare upload capacity, it should be used to make another peer reciprocate. The trick in getting good download speed mostly comes down to sending fast enough to peers so that they reciprocate, but preferably not any faster than that. Now, you need at least that that many connections to unchoke. Note that the division does not need to be even, see the bittyrant paper for details.

The largest number of peers you can divide your upload capacity among, so that they all still reciprocates, or the smallest number that will saturate your down-link The other question that also needs to be resolved is, how many peers should you upload to? The answer here is: Now, what does this mean? Well, it depends on the swarm, and what capacity other peers have, and it depends on how many distributed copies there are in the swarm. The lowest number of peers that will saturate your down-link. The answer to this question (how many peers should I connect to to maximize my download rate) is: Let's assume that you want to maximize your download rate.

If optimal means the lowest number of overhead bytes per payload byte, you want 1 connection (or maybe 0 connections). You also did not specify what performance metric to use. It sounds like you're referring to the total number of participants in a swarm, but your quote is referring to the number of nodes you should connect to.

Bittorrent sync download rate .1kbs