Whatever the problem is, it's not that those specific IP ranges are slow. I just temporarily blocked everything except 74.125.0.0/16 (google's home address), 1

Whatever the problem is, it's not that those specific IP ranges are slow. I just temporarily blocked everything except 74.125.0.0/16 (google's home address), 173.194.55.0/24 and 206.111.0.0/16 (the CDN). Youtube is plenty fast using the CDN. It can be slow to start because it sometimes tries other addresses first.