I have been playing around with lighting a lot and would like to pick up another flash to kick around with. I see a lot of talk about vivitars, sunpacks, and even the SB-24 and what not. I am becoming very overwhelmed in debating if I should buy another SB-600 or SB-800, or which of the vivitars would suffice? I am using nikons system to make it clear. What would be the suggestions from the experienced? Pros and cons?