Looking at the SPCR recommended list:
The Nexus Value 430 is too small.
The nightjar may be undersized, and is hella-expensive for the size.
The NX-5000 gets poor reviews in enough places that I'm concerned about quality control and sample variance.
The modu/pro82+ seems to have a similar quality control problem
The modu/pro87+ 500W is perfect...and impossible to find in the US, based on my fruitless search.
The 650W PSU's are oversized.
The HX520 is loud in the ~350-400W range
I'm out of town and typing this on my iPhone, so it's hard for me to go in more detail, but, in short, other than a PSU from overseas, I can't seem to find a PSU that stays below ~23 dB when loaded up to ~450W. I'm probably going to go with the NX-5000, regardless of what other reviews have said regarding loud units (poor quality control, I'm sure).
I'd be surprised if you get 250w at max load w/ your proposed system -- not a lab stress test but a real use load. There's just no way you'll see 450w. not even close.
Having said that, I probably still would not choose the Nexus value 430, despite my editor's choice -- it's the oddest thing, I have this hunch it's quiet at the cost of longevity tho there's no way to prove that for any of these quiet/silent things w/o long term, large sample size polls. I also don't like its lower than top efficiency... given the asking price.
You could wait for a Seasonic 460 (or 400) fanless. 80+ gold, silent, survived 15+ hrs in a brutal full power test in my psu hotbox tester w/ just one nexus 120 fan at 7v in 22C ambient. (No fan at 400w load) My early sample is working fine in a new pc i've just assembled for myself. (review/fanless psu roundup to come soon -- maybe in a week).