I've got a pair of Seasonic Plats in service, an 860W and a 660W, neither of which exhibit any coil whine.
The 860 is powering a 3930K with a Titan. The 660 is powering a 3570k and a GTX 780.
Personally, I'd put my money into as efficient a power supply as I could afford. If the Seasonic Plat model fits your use and budget, buy it. Excellent efficiency which creates less heat and less heat creation should lead to longer life of the power supply. But what's been so impressive about the Plats is the voltage regulation. JG tested the 660W and got 0% regulation on both minor rails to full output (meaning both the 3.3V and 5V rails never moved...stayed at initial values....damned impressive!) and 0.7% regulation on the 12V rail.
Now, that M12II is a nice power supply and one great group regulated unit. But today, spending my own money, I'll take an independent regulated, outstanding platinum rated power supply over any really, really good group regulated Bronze cert'd power supply. Why invest in a much older platform these days?