A follow-up post:
I GMed a session of Prince Valiant this afternoon. The players each had a "Storyteller Certiificate" from the previous session, and the first episode of the session involved a very strong knight - the self-proclaimed "best in Britain" (I borrowed some dialogue from when Arthur fights Lancelot in the film Excalibur) - who would let no one pass on the road from Castle Hill to Norwich (? something like that, to the north on the Pendragon map) unless defeated in battle by a knight who he would then accept as his lord.
The first PC knight had a go and was soundly beaten (but kept his certificate). The second had a go, and was persuaded by another player to use his certificate for a minor (but renewable) buff, and likewise was beaten. The third martial PC was in fact a mere squire, and weaker in combat than the other two, but (i) was able to persuade the NPC knight to knight him so that they could fight an honourable joust, and (ii) used his certificate to Slay a Foe in Combat, and so was victorious and won the NPC's horse and arms by his victory. This made him the first PC to have a full-fledged warhorse and heavy armour. He also gained a jewelled sword that grants a prestige bonus to appropriate Presence checks.
The next episode involved aiding a damsel in distress, fleeing from robber knights - the third certificate got spent in this one to help secure victory, and the upshot was that the PC who started the session as a squire ended up being wooed by the damsel - daughter of the Duke of York - and marrying her: when they arrived at her castle, he found that he couldn't say no to her father, who was strongly in favour of the marriage (failed Courtsie check on the player's part). So the PC started the session as an under-equipped squire and finished it with the full arms and steed of a noble knight, the son-in-law of the Duke of York with the wedding gift of a fortified manor house, and a reputation as the one who slew the strongest knight in Britain.
I'm coming more and more to enjoy a system (Prince Valiant isn't the only one, but is a good example) where we can get through that amount of content in a single session.
Thank you Greg Stafford!