In my opinion, you are overthinking this. The admissions council is unlikely to put much thought into the specific workload of each semester. Rather, they will care more about your overall grades, as well as the content of the courses. If taking more courses will lower your grades, then you should not do it.
A transcript is meant to represent a student's ability to learn content and a student's work ethic. If you generally have high grades, then the admissions committee will be confident in your ability to succeed in graduate coursework.
In the end, assuming you have adequate grades, the most important part of any application will be the student's research experience and recommendation materials. A student can have perfect grades and scores and still being rejected from top programs if their research experience is minimal.