I own both. Performance is pretty comparable for the most part. 174 has pipe/tuner/clutching, 175 just has clutching (ZRP weights, stiffer secondary, softer primary). When you absolutely, positively have to put the high mark on the hill, the 175 is the one to be on. Not a big difference, but if you can barely make it to the top on the 175 you probably barely won't make it on the 174. 175 takes overall less effort to ride IMO. Both are excellent in the deep powder. Track on the 175 seems to hook-up better overall than the 174 track. Engine wise the 175 seems happier with the longer track, and pulls slightly more track speed in a deep powder climb than the 174 with a pipe. Suprisingly the 175 always burns slightly less fuel than the 174, but slightly more oil (no surprise on the oil). Making a down hill U-turn is definitely easier on the 175 IMO. On an extreme side-hill in set-up snow the 174 is better, but only slightly so IMO. Never had any problem with back end washing out on the 175. Clutches run a little cooler on the 174. I have blown one belt on the 174 (Gates). I have not blown a belt on the 175, although I have fewer miles on it.
Overall I prefer the 175 over the 174 because it takes less effort for me to ride, which translates into longer rides and more fun. Nothing wrong with the 174 though. No problems with either, just add gas/oil and ride.