I work on a medical/cardiac PCU which is actually more medical telemetry than a PCU (no titrating drips, etc.). The ratio is usually 5:1 but it can and very often goes to 6:1 - which is usually (not always - usually) a nightmare.
I work on what I would call a mix of step down and med surg patients. My floor gets vent patients, renal failure patients, kidney transplants and kidney/pancreas transplants, urology patients, and everything in between. On day shift, the ratio is 3-4:1. If a nurse has a vent patient, they try to keep that nurse at 3:1 with no admits. At night, the ratio is 5-6:1, even with a vent, although effort is made to keep a nurse with a vent at 5:1. Although I like working night shift, I wish more effort was made to keep day shift ratios even at night. If I have a vent patient, I spend a lot of time with that patient, and I can't have 4-5 other patients that are trying to climb out of bed or pull at their lines. That's typically my load. 6 patients with a vent would be more doable if most of the patients were alert and oriented, and trying to sleep. Otherwise it's unsafe.