Tell us what exactly you're going to run (CPU, VGA, drives) and you'll get a very accurate prediction of wattage. And knowing your wattage you'll be able to pick the optimal PSU. Optimal meaning that it'll have enough power to fuel your rig, will be ultra quiet (or even effectively silent) at low loads and v quiet when loaded, and will not cost you a small fortune.
After all, there's no challenge in recommending you to get P183 + CP 850
Your reasoning behind the wattage / noise / reliability relation is false, as this thing varies from model to model.
In short - because today's quality, certified PSUs, when powering a certain rig, run under the same conditions (producing practically the same amount of heat with a specific setup), the difference boils down to the choice of fan and setting of its controller, and to a lesser degree on the PSUs radiators.
A 500W unit working at 100W idle load will generate (virtually) the same amount of heat as a 1000W unit.
A 500W unit working at 450W gaming/benching load will generate (virtually) the same amount of heat as a 1000W unit.
The fact that one will be running at <50% and the other one at 90% means nothing. What temperature they'll be running at depends on their radiators and fan RPM. And these things will depend on the make and model.
Also, remember that today's quality PSUs generate v little heat and come with high rated capacitors - which means they'll be operating with a lot of headroom. A capacitor rated at 85 (or 105 in better models) may actually never work at 50 or even 60 or more. At low loads they'll be cool, and at higher loads the fan will kick in and cool them.
Another thing to remember is that unless you're a professional gamer who needs to practice 15 hrs a day, your PC will most likely idle 90% of time.
Sorry for getting theoretical, but it's a common misconception to get a super powerful PSU in hope that'll be running cooler. Actually, it's the other way around. The higher the load on a PSU (up to a certain point, usually around 90%) the better its efficiency. So a 500W PSU working with 100W load will have a (slightly) better efficiency than a 850W unit running at 100W. Higher efficiency = fewer watts wasted = lower temperature = less work for the fan. Of course, 80+ certificate makes sure that a PSU will always have a good efficiency, even at low loads.
See this
page - a table compares various PSUs. All v good, hi quality PSUs made by the best producers. All exhibit v similar efficiency. And all behave differently
