@Morii: Thanks for the well thought out and reasoned post. I will be doing some testing before the tournament goes live but I really don't think the issue is as big your concern. 5 vs 5 is a very small game and allows for much better coordination, teamwork and organisation than (even) an 8 vs 8.
Consider what may be viewed as something of a worst cased scenario: Field by the River, Sarranids (farm spawn) Khergits (village spawn). As Sarranids, what you could do is get the infantry to take throwing weapons and some extra shields for the archers, get the cavalry to go on foot, with a shield and throwing weapons and then move to the castle wall. If the Khergits rushed at that point, you should already have the cover of the wall, with all 5 of your men able to return fire and have protection. If the Khergits are hanging back for the flag, you could move up to the bridge and there's not much the khergits can even do, that wouldn't make them very vulnerable. 2 Horse archers would be torn apart by two decent foot archers that have 3 footmen with them. You can also use the cover of the forest and possibly think about moving to take the ruins, which is a good central position on the map.
Sure, things might get tricky when the flag spawns but I'm not convinced that the advantage is too great to be unplayable. Remember that the rules include spawn and faction swapping too, so both teams will have a chance to steal a round, while the others are playing as Khergits.
Anyway, as I said, I will be doing testing for this. Haven't asked them yet but hopefully I can get CoR to do it at the end of a training or something.
@Heth: Nope, random factions, random maps from random.org. Persistent factions work well for the campaign but I don't think it'd be much fun for the tournament.