BD capacity

I was looking on Amazon and saw that the Bond 50 box set is available for pre-order and it's 23 discs for 22 movies. Over the weekend I bought The Da Vinci Code and the extended cut of the film and special features are all on one disc. So this got me wondering how much footage can fit on to a single BD. I understand that there are single and dual layer discs, 25/50 GB of space, respectively. And I understand that movies have different average bit rates which can create a fluctuation in how many minutes can fit on to a disc. I read on Bluray.com (I think), in their "What is Blu Ray?" FAQ that a dual layer disc can hold 9 hours of footage, in HD, on a disc. So when I saw that Bond 50 probably has the feature film and all special features on a single disc, I was wondering if they were cutting on PQ and AQ to fit everything on to a single disc. Companies like to exaggerate of inflate specs of their products, so I half expect that 9 hours of HD video on a 50 GB BD wouldn't be the best you can get. What would be a reasonable amount of film length for a movie that deserves the highest picture and audio quality, i.e. James Bond, Star Wars, Lord of the Rings, etc.? Would there still be enough space for bonus features with the main feature? Both Star Wars and LOTR have their special features on a seperate disc, with the LOTR EE versions on 2 discs. I admit I've not checked to see whether they movies are on single or dual layer discs, but I would expect dual. Perhaps I'm still too used to the way DVD capacity is chosen.

So how long of a high quality feature film should be able to fit on a single blu ray disc?

Thanks in advance to all responses.

Thanks, I was really wondering about this. I'm very curious to see what the specs of the movies for the Bond 50 box set will be.

Thanks for the replies, everyone. Yeah, my main question, that I understand now, was how long could a movie be before the special features would cause a decrease in available disc space for the main feature. I understand that there are many variables, but for movies that we would expect at or near reference quality, would a movie have plenty of room left for special features. Certain movies have several hours of video not using the main film, I.e. commentary.

So a 2 hr. movie with 10 hours of interviews and documentaries would other have to reduced average bit rate of the movie or the special features. Although I have noticed that most features are only 480 i or p and 2.0 ch audio. So that does allow for an increase in special features run time.