I did some experiments lately with SD overlocking stuff,
After calling sdSoftReset the camera switch from 96 MHz to 48 MHz mode, and AccessMode from 7 to 3, resulting in 21 MB/s write speed, changing preset to 96 MHz makes the write speed ~36 MB/s instead of ~41 MB/s , changing AccessMode from 3 back to 7 makes the write speed ~41 MB/s (now we got back original write speed), from there I could overclock to 160 MHz without a problem, but doing an overclock to 192 MHz/240 MHz makes the camera switches back to 48 MHz (21 MB/s)
After some research I found something (probably related to Bus speed configuration) which changes its value from 0 to 1 after doing sdSoftReset and especially after hitting recording button (after doing write/read processes), I tracked what part of code does that in 700D ROM, and found out it's coming from sdReadBlk and sdWriteBlk, well let's force that "something" value from 1 to 0 using this code (for 700D):
patch_instruction(0xff74c814, 0x13a01001, 0x13a01000, "0xff74c814"); // sdWriteBlk
patch_instruction(0xff74cae0, 0x13a01001, 0x13a01000, "0xff74cae0"); //sdReadBlk
-->I could overclock to 192/240 MHz presets (after a sdSoftReset/after switching to 48 MHz)

(didn't blow up the card or camera . . managed to record several clips and +50 GB of data, everything was stable)
I am not really sure what that "something" does, do you remember these initial 192/240 MHz presets (which were and still not stable):
https://www.magiclantern.fm/forum/index.php?topic=12862.msg228447#msg228447https://www.magiclantern.fm/forum/index.php?topic=12862.msg228460#msg228460Above patch forced these none-stable presets to work, and it didn't switch to 48 MHz . . but I experienced speed drops then --> Card can't be accessed a.k.a "Card full" issue, well we knew those presets weren't stable and we are not using them, but we know current
192/240 MHz presets are stable (on 700D/6D)
--> So from above experiment and results it might be there some
Hope to force 240 MHz on EOS M, and 192/240 MHz on 70D, please try the following sd_uhs.mo (for 70D/EOS M):
Download:
https://drive.google.com/file/d/1DGa2nhSdgu8tSY2Yy22tZQR3PmYpwB4i/view?usp=sharingIf it worked --> you will have stable 192/240 MHz overclock
If it didn't work --> you might experience speed drops while recording and emergency stops, then "Card full" issue might appear (maybe something else?)
-Do this test at your own risk
-If it worked, it's might not be the correct way to force these presets
Edit:
Doesn't work well,
not stable at 240 MHz for EOS M,
don't use it.