I did as you suggested so now the Army looks like this:

ARTHURIAN ROMANO-BRITISH
Corps I
Competent commander (Arthur)
4x Heavy cavalry impact elite
3x Heavy cavalry
2x Light cavalry javelin mediocre

Corps II
Competent commander (Bedevere)
4x Heavy spearmen
2x Medium spearmen
2x Light infantry bow

Corps III
Competent commander (Sir Robin)
4x Heavy spearmen
2x Medium spearmen
2x Light infantry javelin

25 units, 200 points

OK, I'll be in on Sunday.  I know Mike is out so is anyone else stopping by for a game?

Sounds good. You might also experiment with splitting the heavy and medium spear between Corps II and III so that they both can cover small patches of difficult terrain and open ground as well. Matt has had some success with this approach when playing the Byzantines.

That looks like a solid mix of heavy infantry and cavalry. I would recommend some medium spear with your heavies to contest difficult terrain. Also, FYI, this list only has 3+ command points, so you can't have two competent commanders and a brilliant one. You will need to downgrade one of them.

Here's what I came up with for the list:

ARTHURIAN ROMANO-BRITISH
Corps I
Brilliant commander (Arthur)
4x Heavy cavalry impact elite
3x Heavy cavalry
2x Light cavalry javelin mediocre

Corps II
Competent commander (Bedevere)
8x Heavy spearmen
2x Light infantry bow

Corps III
Ordinary commander (Sir Robin)
4x Medium spearmen
2x Light infantry javelin

25 units, 200 points

Arthur and his "knights" can put serious pressure on one of your opponent's flanks while Bedevere and the spearmen hold the center. Sir Robin and his boys find some nice terrain to hide in (ideally near a key point on the battlefield) and generally threaten to pop out and cause trouble (or you can put them in ambush).

This list should do fine against most things, but massed elephants (Classical Indians), cataphracts (Parthians), or shooty cavalry (Mongols) will be difficult. C'est la guerre, however, in this game there are no true power lists.

So, I figured any interested list building for feedback, comments and suggestions can be posted here.