To get a better handle on the size between the TU and the G400C, I went to
http://cycle-ergo.com. They have a model of the Honda CB400SS, that the G400C is based on, so I loaded up that and the TU250X to compare.
The CB400SS is slightly bigger than the TU and looks like it would fit me a little better. If the G400C really is like the CB, it looks like a good fit for me.