Well, I went ahead and bought a few frames - The WA/Footsore foot knights and foot serjeants, and the Victrix mounted knights.
The WA figures are a lot smaller than the Victrix figures. If you put near identical barrel helms from either set side by side, the Victrix ones are fully 25% larger. The WA heads in particular are really titchy. Having just compared with some Fireforge early medieval frames, I'd say FF are somewhere between the two in size and stature, although closer to the Victrix size. I think kitbashing the WA and Victrix sets would be possible when it comes to the arms, but perhaps not the heads.
The other thing I notice is that the detail on the WA sets is much softer and less defined. The moulding on the Victrix set, particularly on the mail, is a lot better defined and sharper. I've noticed before that Wargames Atlantic seem to mould their sets in a hard, shiny grey plastic. You'd think this would result in a sharper figure. Actually, the opposite seems to be the case. Their plastic figures always have a slightly 'soft' look to them, at odds with the apparent hardness of the material.
All that said, they are pretty nice, and I will definitely build a few to add to my Feudal collection (gallery here:
https://leadadventureforum.com/index.php?action=gallery;su=user;cat=755;u=577)
To me, the Victrix figures are superior, despite the excessive creasing in their surcoats - a longstanding issue I have with Victrix's otherwise excellent models. The caparisoned horses are rather brilliant though - bigger and more dynamic than the Fireforge equivalents. I'm now looking forward to the Victrix foot knights and serjeants.