I tweeked a bit with a file and was able to put everything just like in the 2 year per turn mode, but now it's in a one year per turn mode.
Here are my results(in two different games):
The AI is agressive sometimes(although it depends on who you have as enemies) and is for some periods of time pacific.
By the year 1150-1160 the borders of all factions were set, and very few factions have expanded but just little.
All (neighbour) factions by 1190 have used chilvaric knights and pavise crossbowmen with some degree of frequency, but most of their army units are still relatively weak. Siege weapons are used in about 35-40% of all siege attemps and the weapons used are mostly trebuches and catapults.
Only by the year 1220 has the AI started to put heavy mail in militia units.
No faction has disappeared, never, in both cases.
Large /huge cities and citadels were everywhere by 1200, this makes hard for AI factions to lose against ones another and even for the player to expand it's territory and this is the essence of what makes a chalenge for the player to even think of expanding further than this borders.
I've had quite a pleasent time in consolidating my territories, at least in my opinion, the time available before gunpowder appears is long enough for you to have a couple of adventures and to use you most advanced units before new technologies appear.
In short I've really enjoyed playing under a one year per turn mode, the amount of time available seems very good and gives you enough time for you have a very flexible campaing before you can worry about spending more funds in further technological improvements.
However, perhaps 1,5 years per turn also does seem to fit.