User blog comment:B214/Question and Answers 2/@comment-162.202.198.72-20140122105000/@comment-1359322-20140122134053

It's only said that the True Excalibur is on par with the Durandal. Not much is known about the True Excalibur other than that. You can also consider the Ex-Durandal to be a fusion of the True Excalibur and Durandal. So the current "True" Excalibur is assumed to be a Holy Sword with the 7 abilities of it's 7 swords.

As to Caliburn, yes it's more powerful than the Durandal and Excalibur.