Victrix Imperial Guard kits of all types mix very well with Perry but in scale and style. Note though that the Victrix kits are deceptively limited in variety, especially the Guard. There is essentially one "master sprue" from which all of these kits derive. That sprue has only 6 unique infantry figures (2 single-part marching, 4 torsos on which you can add a variety of arms). That section of 6 is doubled on the sprue plus some command figures. Every single Victrix Guard kit then has this sprue in it with only a few addons (different hats for the Chasseurs, an extra sprue of shakos for the Middle Guard). So if you buy a box of Old Guard Grenadiers, OG Chasseurs and Middle Guard Gren/Chass, you just end up with a lot of the same six greatcoat-wearing figures over and over. Obviously "greatcoat with hat" works for just about every French unit at some level, but it will look repetitive very quickly with just six poses.
All that said, they will mix nicely with Perry, Warlord, and anybody aligned to that height.