My first Prime was Transmetal Primal. Second was RID Prime. My first Megatron was actually Gobots Megatron. I just didn't know he was Megatron for like 15 years. I often used him as "Roller" for RID Prime and I assume he's never really forgiven me.
I like to imagine that Orion Pax has his own Cybertronian vehicle mode even though the toy doesn't have it. It would be Orion Pax evolving into Optimus Prime, but Optimus Prime cannot turn back into Orion Pax (even though the toy obviously can).