I really don't think the 5D3 can do 1080p30 RAW in continuous recording for long. The limit seems to be 90MB/s
As mentioned before, my Lexar 128GB 1000x both managed 1080p24 reliably for over 5 mins. My Sandisk 256GB Extreme Pro VPG65 also can handle 1080p24 up to 20+ mins at a time, on top of the 1920x960p30 I mentioned before.
The new Lexar 1066x 256GB is a lot more expensive than the Sandisk but I guess that's because it's new. The specs seem to be the same but I suspect the price differential could be the higher spec demands of the NAND chips.