I understand the benefit for cameras (speed, quality etc). But, is the faster card of any obvious advantage in a 650? (given you can get the originals so cheap)
Yes. Search and you'll find out why.
The Ultra II is vastly superior to the original: Transferring MP3s to the card is much fast as are backups, etc. No contest.
------------------------------------------------------------------------------------------------ Palm III --> Palm V --> Visor Prism -->Palm VII --> Kyocera 6035 --> Kyocera 7135 --> Treo 600 --> Treo 650 --> Treo 700p --> Treo 755p -->Centro