I have the D600, and itís a great choice when I need to fly out a heavy and bulky light/modifier several feet from the stand.
The Impact stand you presently have or a C-stand will handle the D600 boom, but I feel they would be a little light if you were to load the D600 with the weight and counterbalance itís capable of carrying.
When I have a situation that requires the D600, I prefer a wheeled stand with a larger footprint so I can move it about easier. The Avenger A5036CS works well, and is easy to sandbag.
For less strenuous setups, you might want to consider a baby combo-boom stand like the Avenger A4041B. Iíve never used this stand, but it looks interesting.