fuelling on longer rides

Okay, it's a complicated situation. For starters, everyone is different, in their requirements, and how they use their fuel stores, and how much fuel they store. Generally speaking, an average person ( try defining that ) can store about 2 hours worth of glycogen in their muscles and liver ( mainly ) and even that is a finger in the air assumption to an extent. It depends on rider fitness / conditioning and exertion level, but about 2 hours at moderate exertion levels, is most folk's limit. The 'higher Cadence uses less glycogen' thing can be true, but that's complicated as well. In order for the high Cadence approach to work properly regarding lowering glycogen depletion rates, you need to be at a suitable power to make it so. The higher your cadence, the higher the requisite power has to be to make it work properly. It's no good flinging your legs around at 90 rpms ( for example ) if you're not pressing hard enough, for long enough, to engage the fast twitch muscles fibres in such a way that they feed most efficiently, and are dominant in their effect over the slow twitch muscles. It's possible to get some increased glycogen depletion efficiency at lower cadences and power, but it's been scientifically proven that the best effects are achieved at 90 ( odd ) rpms, with the requisite power ( which is higher than a lot of amateurs would probably  be able to produce for extended periods ). The ability to get this best of the best fuel efficiency, is dependent on having the fitness ( VO2 max, Lactate Threshold, Max HR, and FTP ) to be able to pedal like that. A lot of ( more normal than a pro cyclist in terms of fitness and conditioning) riders will find they are actually (glycogen use ) efficient enough, at lower cadences ( 70 - 80 rpms ) with the requisite power at that cadence for it to have some effect, they just won't be as 'super efficient' as the even higher cadence, even higher power pedalers.