...The more I read the more I feel S12II wasn't the good choice. I might explore the return policy of Amazon and get the G-360 or G-450 instead...
All three of these power supplies are fitted with the same fan, an Adda ball bearing unit with a top speed of around 2000 rpm. Seasonic tend to use a fairly aggressive profile with this fan, particularly with the smaller capacity units. So it is important that system power consumption does not exceed 50% or so of the PSU's nominal capacity if fan noise is an issue. To illustrate this point this is the fan profile for the G-360 from the X-bit labs G-360 and G-550 review
Haswell systems have been reported as drawing around 190/200w even when the 750 TI is overclocked and overvolted. So the G-360 should be OK, just. But system power draw is not the only factor is how hot a PSU runs. The fan control is temperature based not load based. So higher ambient temperatures, both in terms of weather and the room the machine it is in could lead to a G-360 just going over into that zone where the fan speed ramps up sharply. The best way of avoid this possibility is to use a higher capacity PSU, say in the 500 to 550w range. The G-550 would certainly be better than the S12II in terms of fan noise, the S12II units were fitted with varying profiles depending on the capacity but tended to ramp up speeds at lower settings than a G series. I cannot find a profile for the S12II 500 but this is the one for the 520w, again from X-bit Labs
If you compare this with the fan profile of the G-550
there is an improvement, reflecting Gold efficiency and later technology. Whether the difference is worth the additional cost over the S12II 500 is another question if you are not going to stress the unit beyond around 200w.