Thanks for your thoughts.
How many frames can you get with your 7D before buffer stutters? It seems to me that fps is not the best metric; maybe number of sustained frames before buffer fills is better performance measure. That, in turn, is clearly a function of shutter speed being used and file size (RAW vs JPG) - and that changes for every shooting situation. The fastest shutter speed is limited by the available light and lens being used.
With my 7D, I shoot my dog chasing other dogs in dog park. On a sunny day, I typically shoot in AI Servo mode at ISO 400 at about 1/250 sec shutter speed and f/8 with 70-300 zoom, which results in less than 30 sustained RAW frames (25 MB/frame) before buffer fills. I'm very happy with this.
I could use even higher ISO with faster shutter speed, and get more sustained frames, but this would reduce IQ. Some performance trades need to be made.
The 7D rating of 8 fps must be quoted for some shooting condition, but I honestly do not know what that is. I could not find any such spec in the 7D user's guide.
Obviously, the maximum number of sustained frames is achievable in lots of light with the fastest shutter speed available.
In the end, I think the performance difference between 6 fps and 6.9 fps quoted for the 5D3 would be very hard to measure. And not that relevant.
Lighting conditions will slow the max burst of the 7D down. I'm not sure if it's true with other cameras or not. But in low light the burst slows to 5fps or so. Bryan at The Digital Picture noted this in his review and suppose the metering system was the bottle neck in low light situations. You can try it with the lens cap on. However, if you are in AV or TV mode you can use exposure lock to "override" it and get 8fps regardless of lighting.