I think the question you need to ask youyrself is 'is your system verging on being too bright with the HD800's?'
If the answer is yes then probably the BW would be a better choice.
If no then the SW will not add to the brightness has plenty of tight bass and extremely detailed and very fast. As the last 3 attributes are HD800 strengths anyway I assume more will be preferred.
P.S I have 3 SW cables for my HD800, LCD2.2 & HE6.
Thanks for the advice.
My headphone amp is Yulong A18 and all the cables I tried (stock cable, Cardas, Oyaide and Scorpion cables) did not show any sign of brightness.
You are right copper cables tend to be slow when compared with silver one. To get most out from HD800 I think I will go for SW for my 2nd HD800.