I have used all three sizes that Whipple recommends for my stock setup. The 3.625, 3.500, and 3.375 The feel for extra power with each size you go down is minimal with each size giving 10 -12 extra RWHP same in Torque My breakdown is as follows: 3.625 = If you want to stay incognito this is the size you want, the Whine/Boost starts at around 1800 to 1900 rpms. Meaning you can drive all day without hearing it if you baby it. It will give you the smoothest ride of all three without even thinking about how you step on the GO pedal. (That is until you mash the GO pedal) 3.500 = This comes standard now and I used this one for the longest time so far, Whine/Boost starts at 1500rpms. If you’re real careful with the GO foot, your passengers will never notice. 3.375 = Is an upgrade option, I think most should try it. Whine/Boost starts at 1100 rpm. If you’re into making noise with chirping off the line at every light and want instant Boost at the slightest tap of the throttle this is the one for you. I have been driving around for five weeks now with the 3.375, it is fun!, but if you drive people around a lot you will turn them into bobble heads if you don’t take care of your GO foot. LOL I wish I could tell you how each one reacts in dirt and sand and rock climbing but as you guys know my Raptor is still a Street Queen for now.