At E-4 you're still required to make get a good enough test as well as enough points on an eval. However that doesn't matter if your quotas are shit. Advancement rates are public so you can see differences where they literally just require you to have a pulse (Any of the Nuclear rates making E-4) or if life sucks and everything hates you (Surface Electrician's Mate (Nuclear) E-5)

Also E-4/E-5 is the difference for having a stupid easy time getting a housing allowance or being stuck in a barrack.