Only fundamental differences are 1) Bigger SSD! and 2) the OCUK spec covers 64GB of memory, but even doubling the memory you've listed, it still comes in cheaper, and like you say, all depends on the build/warranty cost. I'll have a nosey at the bits you've listed. Thanks for taking the time to compile, it's much appreciated.
Antec P8 its a horribly restrictive case with terrible thermal results especially for the GPU you can check a review on gamersnexus youtube, tbh I am not sure Antec has made a good case since the 300 and 900 I suppose the P100 was okay but it was so heavy and not any better acoustically than a fractal design case of the same era. (I don't hate Antec I still have a 300 and I used to own a 900 as well as a mini P180 and a full size P180 I just don't think they are any good anymore)
NZXT H500 is similarly priced much higher build quality and significantly better thermals, I haven't got hands on experience with this case but I have got a NZXT Manta and its build quality is excellent.
Phanteks Enthoo pro M is nice and has better airflow, I have the special edition glass one of these myself for my workstation and I am happy with it but I feel like the back panel is a bit thin especially compared to the fractals that I have.
If you want a quiet case then fractal cases that have solid or swing door front panels like the R6 or define C are reasonably quiet they are more restrictive as they have a solid front panel but they are okay thermally
I have used many fractal cases over the years I currently still have an Define Nano S and a R4 (but I have had multiple R3 and R2xl in the past) which are very similar to the R6 and define C and I am happy with mine I use static pressure front fans rather than airflow fans in the front as I found they pull more air into the case than airflow fans and in the R4 I have used the fan profiles to turn off all my fans below 40-45deg C and I have 6 SSD's and 3HDDs in the case so there's a lot of stuff in the way as well so static pressure fans help push air through the obstruction there too I had used airflow fans before but they had to work harder to get the same temps so in turn were louder and that meant they had to go.
I have also heard that the Silverstone KL07 Kublai is an excellent semi-silent focused case with a good balance between decent airflow (especially for the GPU) and reasonably quiet and while its not typically as quiet as a fractal or be quiet! case it does have the airflow advantage.
the be quiet cases are probably the best silence oriented cases you can buy but they are expensive and more restrictive to airflow so typically run hotter
the Silverstone RL06 is probably the most airflow focused case in a similar price group so you could use it with the fans set to low you could get good thermal performance without too much noise (until the system is on full load then it will be quite loud compared to everything else listed so far)
I guess you should decide based on whether you prioritise low temperatures or silence rather then incorporate cost and looks into the decision.
