The blond on the left is G2F with Body Builder 0.5. The red head on the right is Gia. To my eye it looks like Gia has more arm muscle definition and less leg muscle definition.
What skins were used? Wouldn’t a true comparison utilize similar skins, as in same skin tone? Are there any skins that can be used for both? G2 is very fair and Gia is much darker.
Both are the default skin. The G2F skin is the Bree skin which uses UberSurface. The Gia default skin uses the Sub Surface Shader.
I could use the Gia skin on G2F. The Gia skin uses the Gia UVs, but if you own Gia you can use Gia UVs on any G2F based character.
I’m at work now, so it will be some time before I can try anything different. Lighting could be better too, but I was in a hurry on the way to work.