Are you predicting a preset manual focus point there, or letting the camera autofocus it?
I actually got outdoors for the first time with the Sony A7Rii today, as it wasn't pissing with rain (I'll re-master posting pics again soon). I've only got one native lens for it at the moment, as the 25mm Batis is on back order, so took it out with the "cheapie" Sony 28-70 lightweight plastic-y zoom. I've got quite a bit of learning to do on poking the relevant custom buttons first time when changing focus mode or focus area, but managed to track focus on cars coming towards me at around 30mph in a burst of 5fps shooting,and then was looking the other way when a gaggle of silent cyclists came by
42.4 megapixels is a lot, innit? Its high ISO noise performance is in a different league to my Sony A77 (APS-C), and pissing about indoors at night got me perfectly usable images handheld at loony ISOs such as 56,000 odd, and the image stabilisation is even better then the A77, some 1/5 second shots handheld were fine. Looking at them in Lightroom zoomed in so the image would be several feet across shows perfectly recoverable noise at these silly ISOs, so I expect to do fine at the regency dancing, where I've often had to resort to 3200 ISO, and I'll have the added help of the f2 25mm Batis when that shows up, thus giving me another stop to play with over my previous f2.8 max aperture zoom, and of course the Batis will be happier at that aperture, than a mid-price Sigma zoom. My chances of resisting the 85mm Batis are not good.
The APS-C A77 with the Sigma f2.8-4 17-70 zoom weighs over 1400 grams, the full frame A7Rii with the 28-70 f3.5-5.6 zoom weighs 995 grams. Hmm.