No idea about the Orbit or TomTom but Wm6 is a lot faster and better than WM5 in most devices.
TomTom or CoPilot 6? I always preferred CP but most people preferred TT - until CP7 came out which is far better than TomTom.
On most devices TomTom problems (and there are lots of them) can be sorted out - especially if it is a legal version so you can download the patches, so I'd read up on other peoples experience of TT on the Orbit but for most devices I would recommend a WM6 upgrade.
If no one contradicts your advice today with a tale of their orbit blowing up after a week of Mobile 6, I should be fine now! The phone is off ebay, should be with me by tuesday, I doubt it will come with original tomtom discs, but I do have an original unregistered copilot 6 ready to install, so I may use that instead.
Thanks again for the rapid reply!