Sounds cool! I love GBs and 65s and these seem to have characteristics of both. If anyone cares, I lined up some of the frequency response graphs of some similar Celestions speakers using the graphs on their site. I was bored.
Looks like the Creambacks address an issue some people have with G12-65s-the somewhat dark top end. The CB has a pretty much identical midrange, but a little treble spike.