There is no effect at all and I know why!
The game run speed timer as higher character higher speed earn and at some point the speed when it becomes 0.25 sec the character or any speed won't work because the character you put can't keep upp with the speed and you earn same even if you put x100. Att this point you need to use Auto clicker and remove the auto earn character.
I tested the game on something call Speedkiller which you can speed the game x20 real time global speed and it doesn't work as I said previously
Dmg/Def can be added and remove speed.