It is a 'negligible' time difference in the 1500, probably similar time difference to when the mondo track surface was invented, I honestly give it a fraction of a second in a 1500 since the times the past few years are on par with the several years previously. Not to mention I would expect times to improve over time anyway as the population continues to increase and more people do top level training. But even in the 5,000m and 10,000m I don't think it suddenly starts making a massive difference. If the 1500 is a fraction of a second different then maybe a 5,000m is a few seconds different total for the entire race at best. Either way, I don't consider that a large enough difference to discredit fast times today and to not compare times to previous years. These guys running 12:40's this year are FAST! One of them, Kejelcha, has the indoor mile world record before the new spikes. He was one of the fastest guys ever before the new spikes and still is, not much changed. Jacob Kiplimo ran 26:30's 10,000m with old spikes, he's insanely fast. And he's still insanely fast. One of the best ever with or without the new spikes.