Fun thread to read! I agree that it depends on both your designers and yourself. I'm a slow scrapper--on average I scrap 2-3 LOs a week, and CT LOs take me longer because I want them to be the best I can make them. I'm a SAHM to 2 young kids and pregnant with a 3rd, and I only get to scrap after they're in bed.
I'm on 1 permanent team that I adore, and I recently did my first guest CT spot. It taught me that at this point in my life, 2 permanent teams would be too much. I can handle 1 perm plus the occassional guest spot, but more than that and I feel like I can't give the CT and the designer everything I want to. I can meet my requirements in a technical sense, but not contribute at the level and quality I want to.