I finally broke down and added a Winsor & Newton Series 7 brush to my collection. I decided to start with size 00, since if you're going to get a Series 7, it may as well be able to do super fine work.
Right from the first painted line, it felt almost like cheating. I was painting 15mm figures, specifically painting splinter camouflage on some Fallschirmjager Battlefront figures. The tip of the brush holds so well; I was able to paint the zigzag brown pattern of the splinter camo on 18 figures without having to clean and reform the tip.
So far, I'm very impressed with the Series 7, and I can understand why they are often referred to as the gold standard for miniature painters. Unfortunately, my painting skills will need to continue to improve if I'm to take full advantage of this great brush.