I did a CKD-type diet back in spring before a photoshoot and I reached around 4.4% bf (hydrostatic)...but I also felt very sick...I really don't know how all the competitors tolerate being at 2-3% bodyfat...every time I missed a meal i felt like I was canibalizing myself, horrible headaches and overall weakness, with liver problems (innate for me); I passed out a few times. Also getting down to 5-6% is not very hard at all, but once at those levels body resists very hard losing further, especially drug-free.
I'm at about 6%bf right now, and feel damn good about it...although I'm always cold, especially up here in the North