I have mostly Old Glory Saracen cavalry in my army ( sorry no photos ) , Alongside the few GB metal cavalry I have they look a little slight in stature , but not by much but the horses are a noticeable difference , GB being more chunkier .
The OG cavalry match perfectly with the Perry metals and if youre after a bargain fior cavalry to boost the ranks the cheap plastic HaT Almoravid cavalry are also a good option to mix with OG cavalry
I have also got the OG infantry to be slightly smaller than the GB infantry and while I have both manufacturers mixed in the same units thr difference is only noticed if you look for it as allot of the poses are very dynamic
hope that helps
cheers Tom