to slow it down you put a bigger rear sprocket on or a smaller front sprocket on, so 9 / 42 is lower than 10 /42, it's approx equal to 10 / 47
9 / 41 is approx equal to 10 / 45
I've used a 4rt with both 9 / 41 & 9 / 42 on. Either makes it is easier to ride a 4rt without using a clutch than say riding at 10 / 42.