Have you tried the DIY Loudspeaker group? I know they've done some work with some solid testing of the BGs. Sorry I don't have any other information on their whereabouts on the web.
I own speakers based on BG drivers made by Soundline Audio. Technically these are Planar Magnetic drivers not ribbons as the voice coil (aka the wire) is backed by a mylar or mylex sheet.
As far as power handling -- I use a Cinepro 3K6, Series III (400+w / 8 ohms, 650+w / 4ohms) and haven't kicked off the clipping indicator on the amplifier.
FWIW, the speakers I own use the RD-52 driver for Front and Surrounds and the RD-22C driver for the Center Channel.