Well I can only tell you what I've done as each person is different. I can tell you though the Zone has worked where everything else, even very clean eating has not. I am not a hard gainer at all, I can gain weight extremely easily. In a 3 month deployment I went from 180 to 210 just doing a bodybuilding routine and packed on lots of muscle. Of course I then came home and lost it all. Thank goodness for CrossFit, I have found something I truly love to be a part of, which is probably why I hang out in these forums so much. I love the exchange of information and the intellectual stimulus that can be found here is far above the norm.
I started out on 21 blocks and felt fine, but I knew I was eating a ton, I felt like it. Meals felt heavy and I felt heavy.
So I plugged into the calculator what I wanted to weigh, rather then what I was at. I figured like you, I wanted to lose excess fat and gain some muscle, but my goal wasn't necessarily strength or to be huge, but primarily the metcon effect of CrossFit. So I gave myself a target of 180 from 198. So I plugged in 180 and dropped my blocks to 19, then 18, and now 17. At 17 I'm now at 175, my metcon and strength have both improved dramatically and I'm at 7% body fat. This is where I want to be. A fortunate side effect has been a huge increase of strength and power without even trying to gain it, while losing weight!
Now that I'm where I want to be I then tripled my fat intake to 51 blocks a day. So at each of the main meals I eat 15 blocks of healthy fats, primarily extra virgin olive oil, almonds or walnuts, and avocados. When I first got to 175 I did feel a bit weary when doing WODs but the added fat almost immediately got rid of that. The reason why I and others have used fat is because it doesn't have a glycemic effect, and has 9 calories per gram compared to carbs and protein which only have 4.
I will say though I am extremely adamant about drinking enough water each day. I drink 96oz on workout days + whatever I get at the drinking fountain at the gym. I get at least 80oz on rest days.
Biggest thing, you can be picky about measuring on the zone, or you can measure for awhile then eyeball it. I measured until I had an idea and now I eyeball it for the most part. I probably could drop to 5% BF if I was really picky, but I am not. I only measure carbs that can be easily measured. Unless it is protein powder I eyeball the protein amount. Fat is usually just measured with a teaspoon.
I also do not have cheat meals, which many people advocate. I use what I call "cheat ingredients".
Making a salad? I'll throw on some extra fresh feta cheese for flavor. Or i'll maybe add a whole wheat tortilla shell and make my salad a wrap. I might add some blueberries to something. I've even created a no bake protein bar using Kashi cereal, chocolate protein powder and peanut butter. I am to the point a real cheat meal (I'm thinking Burger King) would make me very sick.
I have to admit, I have read 0 of Dr. Sears books. All the information about the Zone I found in these forums.
Hope this helps!