That's good, it's obviously the key. But I had expected you to gift up the scientific civs to reach knights faster. Could it be that you let Ottomans alone? They were the biggies in my game at least, with ToA. They even pestered me with 3-4 sipahi attacks.
Yes, I gifted the Ottomans and left them alone. (Comparing the dom limit with the sizes of the individual nations showed me, that the main continent + Korea/Mongolia + Scandinavia were more than enough to reach domination.) Additionally, the Ottomans had always been the most powerful AI, so I didn't want to fight them.
I also gifted up the Koreans, because they were only small, and I didn't expect them to cause much trouble. They got Monotheism and Engineering, so I had to complete only Feudalism and Chivalry.
Another thing that helped, was that Rome finished Artemis for me and Entremont the Pyramids...
Interesting that you talk of 1 knight army as being decisive. I had 9 cavalry armies in total, several of which died as Scandinavia proved much tougher than I expected, even using the beserks the way they are supposed to be used. I had to divert troops meant for the Celts twice to avoid being kicked off Scandinavia.
I got 4 MGLs in total: one Army helped mopping up the Romans, the next one I transferred to Scandinavia and another one to the Mongol/Korean continent. (Of course, as I had only galleys, once a continent was finished, the Army was stuck there.)
I got the last leader in Scandinavia at a time, when the Vikings were already down to 2-3 cities. I figured that another Army would not be needed here and that transferring it to Korea (the only other place where fighting was still taking place) would take too long to have an impact on the game. But that was around the same time, when I started meeting muskets in Korea and had some losses. The second Army had just finished the last Mongol cities and was ready to move on to Korea. So I decided to use my 4th leader to rush the Pentagon in Scandinavia, fill a 4th Knight into the Mongol Army and fortify my Knights in Korea until that Army arrived. Using that approach, I was able to kill the 1-2 muskets usually defending a Korean city with the size-4 Army and then finish the remaining spearmen-defenders with ordinary Knights.
Playing 20 minute sittings sounds very ill-advised to me. It should cause you to forget what you had in mind during your last sitting. But maybe it makes no differerence to the big picture since you did so well!
I am used to doing (most of) my "big picture planning" at night after going to bed, before falling asleep... So this wasn't a problem for this game. But the precision of my tactical execution clearly suffered from the lack of concentration in these short 20min sessions: many times I lost a Knight here and there because of careless moves...
Therefore I'm quite surprised that you consider 550 AD a good date?! When I came here, I already expected to find 200-300AD finish dates from you, Memento or Neo666...

Perhaps the good date is due to the fact that for the first time in my Civ3 carreer I applied a trick that Spoonwood recently explained to me: when a horseman finishes in the interturn and the popup for the next build project comes up, it is possible to enter the city screen and upgrade the Horse to Knight, and the Knight will already be able to move right away in the next turn! Previously I had done the upgrade after the build-phase, losing an entire turn's movement.
Another unusual thing I did: I traded Scandinavia a lux and iron for two luxes for most of the game, right until the point where I attacked them. By the time I invaded Scandinavia, I had so large numbers of Knights, that the few pikes I met did not really make a difference... But the huge amount of gold I gained from these two extra luxes allowed me to have like 7-8 cities produce a Knight
every two turns:
- Turn 1: produce 10 shields, short-rush an archer for 40g
- Turn 2: 10 more shields to finish the Horse, then upgrade to Knight for 120g right in the same interturn
Also I had enough ship chains in place, so my Knights were never "idle", moving from one theater of war to the next one without delay. (Will post a map later this evening.)