Well I'd say go for it and if you get one with focusing problems return it to the retailer for a replacement, or you could send it in to Sigma for calibration with your camera body.
I have a 30mm 1.4 and I think it's a little off, but it's not noticeable in any of my photos so I'm happy enough with it. But now that I'm not using it much I may send it and my camera body in to get done what I just suggested.
Don't forget that Sigma also offer a 3 year warranty if you register your lens within 30 days which makes it even more enticing to purchase one.
Maybe I'll get enough cash together to get an 85 myself