I am in process of instaling the Fastrax kit this week and according to everything I have heard it does wonders for these sleds. Ask AKSNOWRIDER about the difference in his friend Doug's sled after the FTX d-n-r. I addition to the d-n-r, the FTX kit modifies your rear suspension geometry to help with the over transfer that these sleds do in stock form. I will report back after I get sled on snow, but, Kurt's kit and instructions are top notch and Kurt is a great guy to work with, he will spend hours on the phone to help you without even having met. Heck, he spent about an hour on the phone discussing polaris mods with me, before I even bought a single thing from the guy!!!! I can't speak of Holz as I have never dealt with them. But, mad love for FASTRAX!