For the typematic delay, I have no clue why it is so slow on Linux by default. Probably somebody has set those values 30 years ago and then nobody cared to update them. I use 'xset r rate 200 40' and when I use another Linux computer, typing feels just broken, super slow (Windows has better defaults than Linux in this regard). The weird part, there is no reason why keystrokes should have such a huge delay. Changing the xset values improves the user experience in a quite dramatic way.