I bumped the ISO up to 12800 for some test shots during the wedding reception I was shooting Last Saturday.
These were color corrected and resized. The shot of the singer also had exposure pulled down 1.5 EV. I don't always worry about making EV adjustments in this situation when using speedlites in TTL. Its just as easy to correct the few aberrant frames in Lightroom.
The wide shot of the dance floor shows two of the three Di700s I has set up. The third is camera right as evidenced by the shadows from the chairs.
I had them set at somewhat different FEC to create some direct. I did not have to change batteries for the entire reception. All the shooting was done at 3200, 6400 ISO. Some tests at 12800.
These speedlites and the A7RII suit my style well for receptions. I want to keep the exposure within about 1 1.5 EV of the ambient so that the mood of the room's lighting is not lost.
There is no noise reduction on these: