FWIW- I have been running the new Dayco XTX and have been comparing it to a 377 and 166. All were tested after 20 miles of break in. Track speed is 5 mph faster on the XTX and 166 than the 377. No signs of abnormal wear on the XTX and temperatures are the same on XTX as the 377. The 166 runs the hottest. Time will tell on the XTX longevity.