CAO 48 any day.
Having worked under a FRMS with no Flight time limits and Fatigue Audit InterDyne software showing the "sleep opportunity", I can say with much first hand experience that it has no reflection of the actual sleep patterns or quality of sleep accumulated.
Takes no account of time zones, or the fact I am living out of a Suitcase away from home and normal sleep.
When you have already flown 100plus Flight hours in the last 28 days, and you are fatigued, much better calling in Sick because as far as the company is concerned, you are compliant on their FRMS/FAID and rostering protocols.