jsuchar

I have a CAT 66DX40G direct drive pump, The pump is rated at 4000 psi at 4 gpm. The bypass valve went bad and I am replacing it with a K7-1 unloader valve. The original pressure tips were 4.5 size. They would not work properly, so I was advised to use 5.0 size tips. These seemed to work well, but another person advised me to use 5.5 tips. I am working at 3000 psi. I am confused as to which tips to use. Can anybody help me? Thanks in advance.