I've completely uninstalled and re-installed wow and I still get the cVar error sometimes. I don't think it is HB related.. pretty sure its one of my garrison add ons.
there shpuld almopst be no benefits between 32 and 64 bit in wow
since the new patch all the settings have been reset and changed.
just play with it o and if you look under the slider that controll the FPS you could change the rendering from the wow client to 100% to 50% so less GPU and CPU stress