My keyboard was also laggy. Turning off pop-up, sound and vibration on key press helped. I also turned off sugestions, auto correction, gesture typing and all the the rest i dont use.
I also dont have any problems with scrolling or laggy response. My settings are 122/604 MHz, SIO scheduler, disabled memory compression.
Sometimes it's getting laggy, like after week or two after last restart. But then i just restart device and it works like charm.
Unlike you i did format system partition before flashing.
btw you just made me want to find and play one of commander keen games :)