I am reasonably certain that you need to use an SDXC class 10 3 card for the 100Mbps rate. SDXC class 10 1 is fine for 60 Mbps.
I take it from your user name that you are in Australia. The best price I've found for SDXC cards is from MSY Computers (stores in VIC, NSW, QLD SA and WA). The last Sandisk SDXC 10 3 cards I bought from them, in Feb, were $AU129 each which is considerably less expensive than most anywhere else. But those cards are probably more expensive now.
I have had enough of the SanDisk Extreme cards fail at this point that I will never buy another one. I have a bunch of 64 GB Samsung Pro SD cards and they have been flawless and FAST, 80 megabyte/sec writes and 90 MB/s reads. Samsung 64GB PRO Class 10 SDXC card at Amazon
On Saturday, I took a Samsung Pro Speed Class 10 card to a camera store to collect 4K sample files from a Sony RX10ii that I'm interested in buying (silly me). I was able to shoot 1080 but the camera balked at even trying to write to a card that didn't support at least SDHC UHS-I. To date, I've been unable to locate a Sony specification that indicated whether the camera would support SDHC UHS-II cards.