Single handed chording is not for speed, it's much quicker to alternate fingers of each hand because you can be moving one into position while pressing another. Chording is also slowed down by having to clearly release all the keys between keypresses, where normal keyboards can have some overlap as long as the sequence is still clear. Also reducing 10 possible inputs down to 5.

If you want to type significantly faster English text, stenography looks like the best approach by a long shot. Not so good for symbols though.

/ off topic.