You need good developers to tackle those interesting questions. There is no answer, because you can only rely on rule of thumb and you must know when to break the rule of thumb.

PEP 8, on the other hand, is to get these good developers to agree on the less interesting things, such that they can use it as a stepping stone to the more interesting ones. PEP 8 requires strict compliance, because if different developer ignore different portion of PEP 8, you end up with nothing.

In short, if you have long lines of code crammed together with no spacing, get them to look pretty based on PEP 8 first before we talk about how easy is this code to test.