Here is a straight forward Sandisk Extreme SD memory card speed comparison test with four different types of cards and three OMD bodies.
E-M1 Mark III has one UHS II compatible slot (Slot 1). Both slots of E-M1X are UHS II compatible.
All bodies were tested with M.Zuiko 25/1.2, mechanical shutter, sequential mode 10 frames/second (PEN-F Sequential H, others sequential L), 1/1000 s, f/1.2, ISO 400, manual focusing.
I put the camera on tripod and started shooting. When shooting slowed down, I stopped shooting and started the stopwatch. When the camera buffer was empty I stopped the stopwatch and counted the frames on memory card.
The results of the test 1 are on Table 1.
In practice there seems to be no difference between 90 Mb/s, 95 Mb/s and 170 Mb/s UHS I cards. UHS II is very fast in UHS II compatible slots: with 10 f/s the camera buffer gets never full and you can shoot continuously if necessary.
E-M1X slot 2 seems to be faster than slot 1 with each card. This is interesting.
I also tested with 15 frames/second (sequential H) to find the limits. Results are on Table 2.