Creambacks are related to the original G12m-65 watt speakers of the late 70s and early 80s. They are a higher power g12m25 variation. They have a deeper low end and a more restrained high end,but still have much of the woody midrange complexity (a bit less high mids than a 12m25 ). They are big, beefy, wide ane open sounding with presence. Very different than the T75s. Think early Michael Schenker Group (first coupla albums), think Judas Priest circa Screaming/Defenders. That sort of tone when paired with a Marshall.
There are a bunch of good clips on yootoob, do a search for celestion creamback. They have become very popular as the resurgence of the g12m Greenback sound has made its way back into the public eye. For people who love 12m25s but need tighter/heavier tones and more power handling, the 65 is a no brainer.