We used to use Warhammer Ancient Battles which unsurprisingly has a heroic element to the game which suits the 'Dark Ages' well. Where it fails is in keeping a line of battle in some semblance of order without units routing here there and everywhere. It was usually wings, centres or the whole battle line that routed and not units here and there.
In my humble opinion
Hail Caesar failed quite miserably on the points outlined above.
Dux Bellorum, puplished by Osprey, has exactly the right
feel for 'Dark Age'/Early Medieval battles. They sprang out of Dan Merser's twenty odd quest for a set of rules that suit the 'period'. You can play with the basic base sizes or up the number of miniatures in each unit and use larger bases so it is very flexible.
I was about to start really getting into the nitty gritty of
Swordpoint but Covid put pay to that. The rules do put a heavy emphasis on the battle line so an elite unit will still find it hard to make headway and smash through, a problem that many rules fail to address.
An extra word on Warhammer Ancient Battles if I may? The
Shieldwall supplement is great if used properly and not maxed out to win at all costs, The
El Cid supplement is much more balanced and it is hard to put together a killer army (a very good thing) but certainly the most balanced and fun lists to play. I have had extensive experience of all the Warhammer Ancient Battles supplements and if played in the right spirit they are really great fun.
Here's a couple of pics of various games played over the years (mainly though not exclusively using Warhammer Ancient Battles, to hopefully whet your appetite.
Solachon from Claymore 2008:Fulford GateHappy dice rolling when you have made your decision