A couple of days now I've been trying to find a simple trick that can fasten my typing speed and, finally, I think I've found it! As you know, speed is very tightly correlated with how many mistakes you do in each run. So, if you only do perfect runs, then this trick won't be for you. But if you're a normal human being, then you'll want to be able to fix your mistakes quicker, and you can do that by not pressing only backspace, but control-backspace to delete whole words. You can thank me later!
Sometimes that command doesn't work and it ruins the whole test. The site sometimes registers double-space and I'm backspacing without noticing that error, keep your eyes peeled for that too.