I personally like the 4.2 for everything it doesnt make a huge difference in my opinion some people say a shorter stroke is better for black and grey like 2.8mm 3.5 is the all arounder and a 4.2 is a power liner / color packer but personally i can get smooth greys with the 4.2 i think that part is more about your washes hope that helped , if you like to hang lots of needle try out a 4.2 man i also like to hang alot of needle so i usually just set my tube flush with the needle in the up position