My other bike is a Suzuki Volutia which is 805cc and weighs 527lbs.
I like the Volutia, mine is pristine - rides and looks great - but I really notice the difference in power. The odd thing is that even though it weighs 152 lbs. less than the Thunderbird, the TB handles better - feels more balanced in slow turns in parking lots, handles curves better - just all around has a better feel.
I always stradle both if I have to move them around, and since the seat of the TB is so low, I really don't notice much difference.
Hands down the TB is the better bike. Love the torque - even if I do have the whimpy 1600 without the big bore kit (that's for you Daz!).
If you are in a position to do it, I'd certainly go for the TB - I'm sure you won't have any problem handling it coming from the America.
"Do what you can, with what you have, where you are." - Franklin Delano Roosevelt