A chain stretch of only 1 % can change valve timing by 4-7 degrees and for each degree ,your engine power band will 'shift' up or down by 100 rpm. The NEW {07-up} roller chain is stronger,more efficient,accurate,etc. plus it has hydraulic shoes that are made from a better material. The old 'spring loaded' springs , fatigue after time {less pressure} and that causes more valve timing changes.LOTS of people tell me that there bike was running good when new or 5,000 miles etc. and then now ,it seems like its loosing power. My 2000 FLHT did the same thing at around 8-10 thousand miles ,loss power and got quieter exhaust. Pulled the cam cover and ,bingo ,not only were the 'shoes' gone ,but the cams {stock} had a .030+ groove wore in them,both cams. To soft ! There is your 'quality control'. Gears are the best if you can run them. Dewey