A switch from a 7D to a D300s is a step sideways at best, probably a slight step backwards according to most reviews and people I talk to with both cameras.
If you can't take the quality of images you like with the 7D, don't expect any better with the D300s.
The only reason I would consider it is if there were lenses you wanted that you couldn't get for your 7D.
If you are doing it to help your knowledge base as a teacher of photography, then that's another thing altogether and if you have the $$, then go for it.





