Sigma 85 1.4 vs Nikon 1.4 d accuracy?

Hi

I need a fast lens for some gig work and i find the 50 1.4 nikon has focusing issues in low light otherwise its great. So i though about an 85. But which has the greater focus accuracy in low light and or high contrast situations?

Fyi i shoot both dx and fx and im talking about the 1.4d not the new g afs as few people here in the uk have them and the gig is friday

Thanking you in advance
Vic