get the SLP`s if its a woods bike that is an ideal woods pipe, it makes great torque earlier in the rev range, yes it signs off earlier (stops making power) but thats when you grab another gear
.if your riding more wide open shit, Sniper CPI or Shearers would be i wouldnt even say better options for your 4mm, they make the power higher up in the rev range, but will wear you down in a tighter woods situation
Snipers rarely come up for sale 2nd hand, people hold on to those, SLP`s almost never, but Shearers and CPI`s come up for sale for around 400 to 450 for clean 2nd hand units
choose your own adventure bro