Conical head tube: does it really make huge difference?
Assume we have a tapered headset with 1.5" lower bearing and a straight 1 1/8" headset. Let's compare two nearest thrust ball bearings from the manufacturer's spec (SKF ): 30x47x11 (dxDxH) and 40x60x13. For 30mm bearing the fatigue load limit Pu=1.6 kN, for 40mm (the nearest to 1,5") Pu=2.32 kN. So the tapered headset can carry more weight or it will work much longer in the same conditions as straight 1 1/8" headset. Additionally, the bigger lower part of headtube allows to increase the downtube diameter and make more stiff front-end. The stiffer front-end gives more precise steering and increases the pedaling efficiency as well.