Though you can't know the peaks, you can get an average bitrate, which is, in itself, a meaningful value. I don't know the art and science behind it, but I do know that it's possible to get some pretty good looking video in relatively low bitrate VBR--witness the content of HBO and Showtime. It's a mixed bag, but on my cable system, it never exceeds an average of 13.23 on either channel with anything I've recorded and some of it is quite decent. Of course, I've been told that HBO and Showtime receiver most of their content for encoding in 24 fps format and very carefully encode it "by hand" for those bitrates, whilst the broadcasters encode to locally chosen ranges at airtime.
Using filesize calculations, I got an average of 9.54 Mbps. There were no breakup that I saw, though I didn't watch every second of it. (The first season was brilliant, the second decent, but the writing made the third unwatchable--for me--halfway through, so I'm not getting involved this go-round :)). I watched the first half-hour or so, and scanned through the rest for the few brief action sequences it contained and watched those--no break-ups, so it was adequate.
I mentioned this low average bitrate on Fox programming to foxeng in another thread and he replied that there were technical reaons for it and that it would not be that way forever. I've sampled it, and most of it in my area has been around 10 Mbps, with Malcolm in the Middle and some NFL games coming in at 12. This gives it the lowest average rate of any rebroadcast OTA on my system: Fox = 10.55 Mbps, PBS = 11.28, CBS = 12.95, NBC = 15.29 and ABC = 17.03. NBC and PBS are mutlicasting, with PBS carrying an SD channel with their normal analog programming in digital form and NBC carrying their new Weather Plus subchannel. ABC has the most beatiful content, but surprisingly CBS has the next best. CSI: Vegas usually looks great, even at an average 12.77 Mbps (over 10 episodes, sigma = 0.28).