The Franks from Foundry are awesome. Only ancients Foundry did better (maybe) were the Assyrians. You are doing them justice. Franks vs Byzantines are an epic confrontation.
Collecting forces for the Battle of Casilinum/Volturnus are on likely to be the cards. I've got enough mini's to do three or four bases thus far. I'm waiting to see if Foundry do a sale this BF or X-mas though as their prices are a little steep.
I'm planning to "go deep" with the Early Byzantines and their various wars.
You're right though, they are brilliant sculpts and definitely one of their most dynamic ranges.