ISO at 1250, f1.2, 50mm on my D700, handheld 1/200. Can push it much further.
I like to embrace the grain, I’ve never been a fan of the “perfect” photo, and I cringe when people talk “sharpness”. Art photography is something I love very deeply, so I am not out for a reality imitating capture, I am out to capture the feeling of the moment, that burst of color and light, the instant of joy or bewilderment. Our DSLRs in general are very powerful photographic tools, sure your photos will get some grain at ISO6400, there’s nothing wrong with that imho. I think this is where grain type comes into play, where the type of grain your camera outputs can affect slightly the character of the shot. That’s a discussion for another day though. For now, push that ISO and push your camera and lens to the limit!