Why are sites like youku and baidu so slow overseas?
The great firewall being between you and the servers doesn't help, but the main reason is that they only have servers in China, not a distributed content network (CDN) like most of the sites you might regularly access (Google, Youtube, Facebook etc) so that the distance between you and the nearest server is quite great.

You should also be aware that they are progressively locking down content on these sites from overseas - they don't want people accessing illegal content from abroad - so long term they aren't your best bet for getting learning material

Check out sites like CNTV - it seems to load fairly quickly for me at least, and they are actively promoting it to international users as part of the 'soft power' aspect of growing China.