To update this topic - existing customers are getting the V6s fitted either in late December and January.
Now I won't say much about the design - it's dwarfed aesthetically by the original TiVo, but I was adamant that it would be faster than the original.
It is - I've tried out a V6 box at the local Virgin store in my high street, and it is far more seamless and fast compared to the original TiVo with regards to the original UI. I found browsing the TV guide and launching the menu to be speedy for the most part. The on demand menus are leaps and bounds faster on the V6.
Compare to my initial use of the original TiVo back a few months ago, where browsing some of the menus and iPlayer took an eternity.