I've read about the first 5 pages of this and thought I'd chuck in a few anecdotes - both on the academic side and on the job-finding side. I claim the following to only be valid for Cambridge science courses and for investment banking.
Regarding difficulty of the degree, I believe Cambridge is a lot harder than even other top universities. Friends who did a lot worse at e.g. STEP back at school ended up getting triple firsts at Warwick/Imperial/etc. Without exception all my friends who got 2.2s in their degrees and went on to masters courses at other universities ended up getting the top grade possible. Probably the most ridiculous example of this is a guy who got a 2.2 in Maths at Cam, did a masters in nanotechnology at KCL with no prior knowledge of the subject and was the only one in his class awarded a distinction. On the flipside, people who come to do 4th years at Cambridge from other universities will almost always have firsts and on average perform a good deal worse than home-grown undergrads with 2.1s.
Weirdly though, foreign students who come for 4th years in Cambridge seem to do just as well as the home-grown lot, even if they're not from the most well-known institutions in their country (e.g. non-Ivy League Americans). I don't know why that seems to be the case for other countries but not the UK.
Now on job-finding, on one side of the coin the computerised systems most recruiters use will simply reject you outright if you put your degree class as 2.2 or less, Oxbridge or not. Nevertheless I know a fair few people who have managed to work around the system by speaking directly to HR or forming relationships with people in the bank. I even have a mate with a 3rd who's on the grad scheme at a top name house. In these cases dropping the Oxbridge name certainly helped cover the stigma attached to the class. I would think though that any other top university would help in the same way - but I can't be sure.