For those of you interested in wargaming these periods and have been living under a rock here are my two pictures regarding miniature lines and scale.
In order: Gripping Beast Jomsviking(metal), Gripping Beast Plastic Hirdmen, Wargames factory ancient german, and a Bretonnian Men at arms. All of the miniatures are in my humble opinion compatible. The heights are all relatively the same. However, Wargames factory sculpts tend to run on the thinner side. Gripping beast has done a good job of making heads and hands larger making for better miniatures for both ease of painting and aesthetic appeal. Some of the wargames factory heads' have details that are far to small making the miniature look slightly awkward.
In order: Bretonnian Knight of the realm, Fireforge Teutonic Knight, wargames factory celtic cavalry, and a games workshop standard horse model. The wargames factory horse is by far the smallest. Which is appropriate for certain applications. Steppe horses were smaller than western european horses, and ancient horses were smaller then the warhorses of medieval europe (both are more akin to ponies). GW models are always more heroic in scale, the standard GW horse less so than the Bretonnian warhorse. The fireforge horse offers a good size for historical 28mm gaming.