yes, I played BTP extensively in 1.6.4, and i'm testing it now. it's shaping up to be pretty fun. Thaumcraft and Railcraft are both going on as soon as they get a port. the guy is creative, and with modtweaker, the custom block mod, we'll see
So many of you know, the current Cauldron build active (mcpc+) is the last 1.6.4 one they are building. They're now focusing on 1.7.10. So if we get enough mods converted, we may look into going to latest.