Last I read about it the performance was directly linked to the size of the network. In Freenet, if I remember correctly, larger number of nodes with the same content is proportional to the speed of the content download. And the content spreads to other nodes automatically, so if the network is big and demand for the content is big the content becomes very quickly downloadable (it's both "near" in terms of hops between nodes and there are more nodes with better bandwidth).

So I think that such networks will be niche until enough governments try to censor internet at once. This will make enough people interested in networks like Freenet to make their performance ok. I would like for Freenet to be adopted much faster and on a greater scale without some cataclysm for free speech, but it doesn't look like it's possible :(