I'd like to chip in here. On different tracks I sometimes had a slight preference for the sound of the GG or the BH, but overall I had a slight preference for the sound of the BH.
This impression was pretty fairly arrived at as each amplifier had the same power supplies (all golden ref), wiring, volume attenuator and casework. The GG did have 450v supplies and the BH 400v. The volume was equalised as accurately as possible.
It was a wrench but I had to part with one of my babies as couldn't justify keeping both, so the GG has gone. I did hear the new 009S with it and the combination was, on a short hearing, near perfect.
I have noticed after many builds of Kevin's designs my preference has been for the versions with tube OP stages.