Well the repeat rate itself is not the problem. I have a keyboard with a hardware repeat rate of 125 characters per second (quadruple the standard, not just double) and it works fine with W:A. I have it plugged in as a PS/2 keyboard though, not USB.
A USB keyboard should not be messing with the repeat rate; key repeat on USB keyboards is handled by the OS. So a keyboard that does somehow change its repeat rate is probably doing it in a weird and bug-prone way, which even in apps that seem to support it fine are probably clumping the repeats on a smaller time scale.
I recommend turning off your keyboard's 2x repeat mode, and instead use something like CyberShadow's
KeyboardEmperor.
If you can't build KeyboardEmperor from source yourself, here is a prebuilt binary:
keyboardemperor-objfre_win7_amd64.7z - this is built for Windows 7 64-bit, and is hard-coded to a repeat-rate of 100 characters per second and repeat delay of 200 ms. It is an unsigned driver, so you will need to boot Windows in test mode to install and use it (
see here). It may or may not work in Windows 10.
Edit: An easier way is to use
keyrate.exe.