I understand the difficulties in properly sizing a power supply. But where I have always thought that power supplies had horrible efficiencies under 20% of their maximum loads, a couple of people on this forum pointed out to me that many modern high quality power supplies keep an efficiency above 80% to well under 10% of their maximum load. This makes the selection
a lot easier, because you want to go with a high quality power supply anyway.
I am guestimating my SuperMicro X10SDV-TLN4F mainboard with CPU and memory is ballpark the same consumption as the E3-1230v3 example in the opening post. I will have 5-8 drives, of 21 Watt each and unknown spin-up and idle consumptions. I'm pretty sure that setup will not go below 50 Watt idle in total, making the Seasonic SS-500L1U a good choice, with >80% efficiency at 50 Watt load. This guy has tested this particular power supply:
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=276
I think it's smaller 400Watt sibling may be a good choice too, but may be cutting a bit close at peak load with full driver population. However, with power supplies offering better efficiencies at idle loads, there's no longer a reason to purchase the smaller one.