How is Capgemini perceived as an IT Consultancy? How would it rank compared to ACN, Deloitte, IBM etc? I'm guessing it would be something like ACN, DC, CapG, IBM, ATOS, ...Is the brand well perceived outside of the consulting industry? Or would ACN or DC be noticably more prestigious on my CV?

All consultancy firms but different beasts - from the way they are run, different cultures and organsiational set ups. Experiences employers will have had with these companies will influence opinion.