The Rhodocks are anything but "peaceful" in my current game. At one point, they were at war with the Nords, Khergit, and Vaegirs simultaneously. Now they're down to just one war.
I'm playing as a member of Swadia this time, but fielding an almost entirely mounted army composed mainly of Khergit troops (one of my castles was formerly Khergit), with a small band of 5 Swadian Knights and a few more Men at Arms for punch (any more than 5 Knights might as well be called "cheating"). My garrisons are a bizarre mix of Swadian foot troops, captured and converted Nords, and freed Rhodocks, with small numbers of freed Vaegirs and Manhunters, plus a couple of token peasant farmers and women to tend the place.
It's actually surprising that a Khergit army can assault a (non-Rhodock) castle at "reasonable" odds well enough, but more surprising how pathetically they defend it. On offense, they pick the defenders off the walls at range, and the Lancers are armored and shielded well enough to conduct a serious assault. Problem is, when the initial shock wave of Lancers runs out of men, the rest of the army is a bit soft and squishy. Generally, by that point however, the opposing force is thoroughly pin-cushioned. On defense, the combination of lack of shields, too few hard-hitting melee weapons, and decent armor for most of the troops is usually fatal.
Granted, the Khergit aren't the "ultimate army" by any stretch, but extremely effective at drawing off elements from a much larger group of warbands and destroying them piecemeal in the open field, with or without the help of other factions' troops. A typical foot army might have no other choice than to engage all of those warbands at the same time.
Rhodocks seem to be the best on castle defense, Nords on castle offense, Khergit in the open, and Swadians as a decent compromise in every respect except those overpowered Knights. I've yet to find a "strength" to the Vaegirs, although they seem to have an average example of just about everything.