Cat Food and the Guaranteed Analysis?

I'm looking for a great cat food brand. I've done research, and I understand that the quality of the brand and the protein has to do with reputation and reviews and recalls. I understand dry matter calculations and the importance of the ingredients (what you want and don't want in a cat food). I understand that it's essential to have things like protein, fat, vitamins, taurine, and other minerals in their food. However, when reading the labels, some of the percentages seem VERY similar. For example, magnesium, when rounded to one decimal place, is usually about .1. Fiber seems to be between 1 and 5. I know that more omega 6 and 3 fatty acids are good for health of coat and skin and other developmental things for cats. However, I'm not sure what to think about fiber and taurine content and things like sodium, calcium, arginine, etc. What's high? What's low? What's a big difference and what's a small difference? Is more less? Is less more? Is there an ideal range? I need actually numbers, and that's the only thing I cannot seem to find ANYWHERE. For example, let's say I want to compare two cat foods. One has 1.3 % fiber, one had %4. Cats don't NEED fiber, but it aids digestion somewhat and a small amount is good. So is 5 still a small amount, or is that considered high? And if it's not, is it better to go with the 1.3 than the 4? Calcium is even worse, since they seem to be just between 1 and 3. Is it just important that it's included, or should I really be looking that closely at the numbers other than fat, moisture, and protein? I get that there are other important factors, but I want to understand the numbers I'm reading when I look at the products. Somebody help!