I use a connection with 50 Mbps downstream here in Central Europe. The distance to next CDN server is about 250 miles (400 km). I can connect to the city where that server is located with 47 Mbps down and 9 upstream and a 25 ms ping time. I checked that on a speedtest site.
The transatlantic connection was much slower. Ping time to Phoenix server is about 190 ms and the bandwidth varied in a wide range.
I tried the CDN improvement with Second Life viewer, Firestorm, Singularity and Alchemy, it works great on all of them. I didn't have any of the issues mentioned in this thread.
Second Life and Alchemy viewer already support http pipelining feature and that makes them even a bit faster, but the CDN improvement also works on viewers without http pipelining.