It all depends on where you ride and how you ride, it is not just about top end loss. We ride lots of hardpack low snow conditions, miles and miles of 100 + mph at a time. I swapped out the 1.375 for a 1 inch due to heating issues with hifax and (to some extent) idler bearings, along with the associated noise, vibration and loss of top end. In my experience close to 1/2 inch of lug is gonna make more than 2 mph difference. I would say 5+ mph would be closer, it has always struck me funny whan Greg said 2-3.