Going off the topic title, am I right in thinking that you're looking for rules for roughly the 400-1000 AD period? Are you thinking of mainly gaming in Western Europe, or going east and south as well? I feel like there are a number of 'bronze age to Wars of the Roses' type rulesets that work well enough for the period, but may not capture a specifically early medieval flavour, if that's what you're looking for.
Dux Bellorum acknowledges the limitations of the period – lack of scope for complex manoeuvre, the fact that most armies are pretty similar in terms of technology and training (a lot of guys with beards, spears and shields) – and instead argues that successful generalship in the period means motivating troops to fight harder or be braver at pivotal moments in the battle. Leadership points represent this abstractly as a limited resource that you can use to boost your troops, and using them correctly is the meat of the game. This fits with my conception of early medieval warfare, and I also think it makes for a pretty good game. It also works with any scale since 'units' are bases without a specified number of figures, an army could be 40 15mm figures on 4cm bases, or over a hundred 28mm figures on big 12cm bases, and the game would still play the same way.
I'm still building forces for Saga, but it seems like another ruleset that does a good job of getting the feel of an early medieval battle right, but it does so in a different way from Dux. It leans hard on archetypes to distinguish one group of guys with beards, spears and shields from another, and the battle boards seem to bring across the mixture of aggression and cunning that you see in Icelandic sagas.