Someone determined with maths that, on Gold, Marauders use a level 24(maybe) Phaeston and Nemesis use a level 200-something? (can't remember at all but really high) Raptor.
Edit: I might be able to find the numbers, but I'm feeling lazy. Also, I seem to remember the codex saying the Nemesis was equipped with a Widow, even though they are obviously carrying a Raptor.