I am a big "fan" of Gallien-Krueger amps. That are my favourite amps. But I am also a big fan of tube amps. I've been testing various overdrives for twenty years. But I haven't found the perfect OD for myself yet. Recently I've been testing pedals with transformers. They could be the right way.
The 800RAIL sound good. A lot of OD-variations are possible. But it doesn't sound 100% like an 800RB.