I have shot with the D300s and D7000. Not exactly what you are considering but I think close enough to comment.
The D7th is an amazing camera and I am sure the D7100 is as well. However, they are very different cameras compared to the D300s. The body of a D300 resembles that of D800 in terms of size, buttons, etc. The feel of the cameras is totally different. Although the menus are very similar, the external buttons and size make it totally different shooting experience.
D90 to D7000 to D7100 is a natural progression and an upgrade. Similar size, buttons, etc....D300 to D7100 is basically changing cameras. You will not blend right in. If you want to make a total switch, then I would consider it. If you are set with the feel of the D300, then wait for the D400?? or go to a D800.