Loads of good advice, black nips tend to be useless for some reason. seen (first hand) lost of spesh black nips broken and snapped (at the threads like said above) and one or two spokes (again spesh and giant) broken on the threads.
i had some 717's on DTSwiss black spokes and they were great. (consider i flattened some machine build 317's to a pancake and totalled a 321 handbuilt) i currently have 325's on some Alps wheels and my normal wheels are 719 (but i am in the process of changing to 819 as sadly i have become a tubeless convert, after all i said about tubeless being bollocks and people are just "thinking" they feel a difference i getto's some tyres tubeless and i'm converted. more grip, i don't want to run lower pressures or that stuff as i like my 30ish psi but i have more grip over roots and no pinch punctures! so thats me converted, and fyi thats not a "i think i have" more grip over root's i know i have, round the wyre forest we climb up a cross root'd section so i know how much grip my old setup gave)