There are some differences in the pipes. You need to look at the 2607 as a more linear power pipe. The power will come on smoother and more progressive. The 2617 pipe will basically run up fast. The power band is moved to a smaller window you would say for a lack of words. The power with the 2617 pipe comes on fast and harder. Smaller time frame to get onto the "pipe" Sharper ,more quick accel. They both will let the engine run up to the top just how fast the elevator will get you there. Hope that clears it up a bit. Also it is very hard to tell a driver what they sahould use. You drive a specific way and what feels good to you when the car works may not to others. Unless it is a noticable difference both pipes would work. Just what feels good to you is what matters.