Ok. I have a SB-600 that I use with my D40. I want to add another, off camera flash. I know I need to get a SB-800 to use as a commander if I want to use the SB600 wireless/off camera but... Here is my question. I would like to save money. What features will I lose if I just buy another SB-600 and get a 3rd party, flash sensitive wirelss slave to use with the off camera SB-600? I am very happy with the SB-600 and I would rather not pay the price for an 800 if I can get by with another 600. Thanks for your advice.