I am not 100% sure but I believed the bodies changed over time. So parts from one version may not fit into another.
Yes I have heard several times that the later model G250 Graphite has better gas flow characteristics in its case structure than the base G250.
I have one of both, but the cases are identical inside... unless the slightly different Flow Vane profiles make a difference?
Early ones seem to have a parallel blade, later ones have a 'scoop' out of the blade like in my pic above.