I'm not one of the "legends" the OP refers to and I don't have a scientific approach based on heart rates or zones, but basically my pacing rule of thumb for longer rides is "slower than shorter rides". Most of my rides, especially anything over about an hour, are over roads I ride frequently. So I'm familiar with the pace I typically ride in different sections (and conditions). If I'm going for a ride that is substantially longer (say 20% longer) than I have been riding, I consciously trying to keep the pace slower than normal over the first half of the ride or so. How much slower? Maybe back off 1 gear or the equivalent perceived effort. This approach seems to leave enough in the tank for not fading too badly on the later parts of the ride.