I have listened to this video about 3 times, in HD, coming through a large decent sound system.

There are clear noticeable differences in each video in the sounds of the voices being compared.

To me it doesn't portray the T5 as "better"... just different.

Yamaha has used the same sound engine on the T4 and the T5. All that seems to have been changed is EQ'ing, and effects...

yes there are new voices on the T5 but alot of them are accessible by upgrading the T4 using the premium voice packs...

Heres an example:
http://www.yamahamusicsoft.com/en/category/Voices/product/1217427?currency=USD

Have a listen to this:
http://www.youtube.com/watch?v=PZNdBYfNIKI

and this:
http://www.youtube.com/watch?v=ShQ-3jDI0Vc#t=18

and its only $135.00 for the entire pack (I am not a secret sales rep working for Yamaha btw) lol

Nick